Um, no. I don't want to be worse in the straitjacket. I want to be better without it. Nerfing myself, even if it's just one level, isn't the way.
I was assuming you'd be extremely highly optimized, as "dude who fights real good" isn't a "powerful" character in D&D and PF. So with the bio suit, you'd be highly optimized but chained to mediocre physical stats, out of the suit, your full power is unleashed.
But fine, if you want to think of the straight jacket form as normal and it off as a short term powerup only, rather than straight jacket as a gimped version of "true you" and jacket off as true you (which makes far more sense, IMO....), then...
Take some in Alchemist (Vivisectionist, and either Beastmorph or Internal archetypes, depending on what you prefer). Refluff the mutagen so that "drinking it" becomes "tearing off the jacket" and the hour spent brewing a new one is spending that time dedicated to wriggling inside of it and struggling, loosening it for when you do
drink the mutagen break out.
Gives a flat +4 Str and +2 Nat Armor (albeit, it does nerf Int by 2 while it's active) and lasts 10 min. per Alchemist level, long enough for a proper rampage, but still far from an all day boon.