Just to add to the above solution.
This is one of the most rewarding and satisfying experiences Ive ever had playing a game on the most difficult setting. The most difficult part of the game is the beginning. If you can manage to get through that when you have poor equipment etc then you will have done the most difficult section.
This achievement does stack so you will also unlock the Hardcore Henry achievement. I strongly recommend you do this on a second playthrough, the most difficult aspect of Hardcore is positioning yourself and reading the map correctly. So having a good understanding of locations is important. I also combined this with the Mercy (no kills) achievement & Virgin Achievement. So I focused heavily on Speech and Charisma and avoided combat whenever possible.
Alchemy recipes can be found here, these will help until you level up. ://kingdomcomedeliverance.wiki.fextralife.com/Alchemy+Recipes
As well as negative perks there are other massive changes in Hardcore mode. The main changes are: There is no Autosave, No Fast Travel, No player Icon on the Map meaning you have to work out your position on the map, No Waypoints - So you are unable to place a mapmarker. The compass is severely restricted. Health & Stamina Bars do not appear on screen.
Start a New Playthrough in Hardcore Mode and make sure that you select all negative perks. Below I have listed the negative perks, their effects and how best to counter them.
1, Brittle Bones - You suffer much worse injuries when you fall. This can be minimised with the Featherweight perk under the Agility Branch and by improving your Vitality Stat. Use all ladders and stick to roads, try not to go down rocky or steep hills particularly when your stats are low.
2, Claustrophobia - Wearing a helmet with a visor weakens your attacks. This one is very easy to offset, simply wear a helmet which does not have a visor.
3,Consumption - You have Less Stamina and it regenerates much more slowly. This has a huge impact at the beginning of the game. Purchase the Marathon Man perk ASAP. Seven Mile Boots Perk under Maintainance is a massive help Increasing your vitality stat also increase and improves Stamina and regeneration speed. Brew the Buck's Blood Potion. As you level up it will get better. Keep picking Nettles until you unlock Resistance under the Herbalism Branch, this gives a Permanent +2 to Vitality.
4, Haemophilia - All it takes is a scratch and you bleed like a stuck pig, the bleeding is faster and harder to stop. This one is really tough especially at the start of the game. One cut from a sword strike can kill you in seconds. Other than avoiding combat you can counter this by buying the Thickblooded perk. Equipping strong armor is essential. Brew Aqua Vitalis, Marigold Decoction, Lazarus Potions and ensure you always have at least 10 bandages on you and more in your saddlebags.
5Nightmares - Everytime you sleep in a bed you will wake up with stats reduced by 2 temporarily. This has a massive impact initally however once you begin leveliing up is affect is reduced. You can counter this with Insomniac Perk Cockerel Potions, Saviour Schnapps .
6, Numbskull - Lowers the Acuisition of Experience. This is without a doubt the negative perk which has the biggest impact on the game. Eg I picked over 500 locks and my lockpicking skill was only 16.
7, Shakes - You get the shakes which affects archery, pickpocketing and lockpicking. This can be offset with perks such as Deft Grip & Lasting Lockpicks,. Focus on building up your stats in those areas. I only pickpocketed Wayfarers and those sleeping until I increased my skill level.
8,Somnabulent - Sleepwalking. Occassionally you will awake in a random area but usually it is on the outskirts of the area where you sleep so don't worry if you sleep in Rattay you will never wake up in Uzhitz. I did not find a way of countering this one.
9, Tapeworm - You are eating for two. You get hungrier quicker. This like numbskull has a constant effect throughout the game. Buy the perks Ascetic & Human Dustbin Asap.
To check you have activated them all go to Main Level where you normally choose the perks and you will see all 9 negative perks.
The most difficult portion of Hardcore is the beginning when you have no positive perks, poor equipment and low stat. Choosing the right perks is essential, Ascetic, Insomniac, Marathon Man, Empathetic anything which boosts charisma and speech. I chose Golden Tongue as I was completely avoiding combat.
A major tip - Work on pickpocketing & lockpicking from the start. Sell everything to Peshek and build up his cash reserves.
Focus primarily on getting through the main campaign. While no fast travel, map markers and a limited compass were the biggest drawbacks they also really change the experience of the game eg I can now travel in pitchblack from Rattay to Pribslavitz to Sassau. I know the terrain like the back of my hand.
Make use of all the save slots as you may need to go back a few slots, so never playthrough the entire game using the same slot . I would say the most difficult portion of the game is the beginning when you have no perks and poor equipment if you soldier on and level up the experience becomes much easier & will be a rewarding experience.
I combined this with the 0 kills achievement and Virgin achievement. I strongly recommend you focus on Speech and avoid combat particularly at the start of the game when you are weak and have no equipment. When starting the game and speaking to your mother choose the speech bonus. The best way of increasing your stats is quickly get through the first couple of missions until you can train with Capt Bernard. Keep fighting with him until you have a couple of points in each stat.
EDIT Also shrines and crosses come in super handy as landmarks to help finding the right location.
Make sure that when you face Runt you have levelled sufficiently, mastered the Master Strikes Move, clinch also have the bonus skill which impoves clinch by 40%. Visit the Captain prior to the mission and boost your strength, stamina etc and make sure you have heavy armor equipped, and take a shield. I made the mistake of being underprepared and the one on one battle with just Runt took me nearly an hour, all I could do was clinch and counter then runaway until my health stabilised, after an hour I must have inflicted hundreds of small cuts and eventually he died.
EDIT. A commenter has said that their save file on the Runt fight corrupted. As I mentioned earlier always alternate save slots, everytime you save choose a new slot, not only will this protect you in case you need to go back earlier in the game but will protect from corrupted files.