Besides biotics to improve his defense, make it a goal to collect the best light armor out there. Since you can only use biotics, get a teammate with the tech talent, Electronics, so you can unlock secured crates that may contain good armor; make sure to sell anything you find that's no longer needed to merchants, so you receive more money and are able to purchase any light armor and upgrades available.
The Charm and Intimidate skills can also help you at the shop. The better your Charm is, the less items will cost; the better your Intimidate skill is, the more vendors will pay for your goods.
Accessories called armor upgrades can be applied onto your light armor; since the Adept has a weak defense, you should wear the best upgrades. They can give the armor you're wearing some additional bonuses, from health, shields, regeneration, and biotics and tech protection.