I think your squadmates are hardier than you regardless of choices - because they are AI. Biggest things for combat are to use the cover system well, avoid prolonged exposure and use your jetpack well (horizontal is great too). I personally love a sniper/AR combo early, and pair that with biotic talents like singularity, throw and shockwave. Unshielded enemies are easily kept at a distance by the biotic powers, and sniper can pick them off. A good AR (or even a rapid fire SMG style pistol) will chew through the shields of the tougher guys fairly quick, allowing you to gun them down or again use biotics to fling them away. Barrier is also a nice defensive biotic talent. Lastly, Cora has a nice defensive shield talent that may be worth investigating if you normally leave her on the sideline. Lastly, I did find around level 20ish that I was getting better armor/weapons and maxing out skills to the point that I was dying way less. Even tougher enemies didn't bother me so much. I'm around 40 now and death is a rarity. Think I play on the normal setting though - I like just a hint of challenge to keep me honest, but not enough to really slow me down/frustrate me. I play more for story and feels than to pretend I am some kind of pro gamer.