Overview of pure survival:
Pure survival is a game mode where you cannot find ANY weapon parts, upgrade circuits, med packs (other than a few medium size packs) or ammo. In this mode you have to craft everything you use. The exceptions to this rule are medium med packs, the original plasmas cutter & sub machine gun from level one and any DLC items you may have.
I actually found this difficulty quite easy. The reason is because of a few factors:
1. Good quality circuit upgrades are available to build right from the start.
NOTE: This may be because of previous game completions etc.
2. Even though you have to create all of your own ammo, med packs etc you can upgrade your RIG much quicker than usual. This is because you get lots of resources, and more than you would by selling actual items.
NOTE: Going for armour and health are obviously the most important ones to start upgrading. Air in this game isn't needed much so you could leave it, and the same really for TK. Therefore I'd suggest then moving onto stasis upgrades.
3. As the only items you can pick up are components and medium med packs you can easily sell the med packs for somatic gel and make large ones. Also if you have the max inventory you can have say 10 Large med packs and 10 ammo boxes and you'll be sorted for most encounters with 5 slots spare for any medium med packs you find.
NOTE: An easy way to unlock all inventory spaces is to equip the 'legendary engineer suit' from DS1. You unlock this after completing the game once, so if you're doing this mode you should have it. Once the spaces are unlocked you can switch back to whatever suit you prefer.
4. If you only use the plasma cutter or as I used the Evangeliser (Pre order DLC weapon) you can quickly upgrade it right from the start. My evangeliser had 8x 2+ 2+ cuircuits by chapter 7, and I had a fully upgraded RIG by Chapter 9.
5. Also save up your ration seals till you get 60; always sending your bots out to get resources from resource spots (you'll hear a noise chime). You can then go to a bench, select downloadable content (Y button) and buy an Epic weapon & resource pack with the seals (X button). This will give you more resources than you'll ever really need on top of what you find in the game.
1x Epic pack contains:
2000 scrap metal
400 somatic gel
Keep your health and ammo stocked up and this is no-where near a hard achievement.