Yeah I always have one astronaut and 125+% but the third Biome still destroys me, today I went to the final room with an astronaut, great carbine, 4 healing items and even a regen when low on HP...The third biome was were I struggled the most. For similar reasons. My gameplay style does not mesh well with with the pistol or shotgun. Have you had any luck extending your integrity or finding an astronaut?
The room went on lockdown, 5 Kamikazes and 2 giants appeared, all my items were gone :(