I drove Socorro in a 3 mil shorty with a long sleeve rash guard in March. Others were in 5 mil suits but no one wore a 7 mil. Water temp was in the mid 70's. This is probably a bit warmer than the Galapagos.
There is a hard bottom on all dives but it can be at or greater than recreational limits. You should be able to comfortably descend and then become neutrally buoyant at a specific depth, rather than needing to go right to the bottom
A hard bottom at 200 feet == No Bottom. In Socorro you visit Roca Partida which is a near vertical pinnacle with no bottom where you will likely spend two full days and at least 6 dives. You dive in blue water with the Mantas, Sharks, and Dolphins. They will draw you deep if you don't watch out.
On every trip I've taken there after a few days some people start ditching their 5mm suits for 7mm. Everyone has a different tolerance for cold, so bring layers like a hooded vest you can add as needed. I've been happy with a 5mm and Lavacore vest with a 1mm hood in both locations. My wife uses a 7mm and a vest + hood. Next time she'll bring her heated vest.