There are a couple of large muscle clusters that you could focus on that will keep your lmm% up without feeling like you're getting too bulky. I'm still pre-op, but because I have heart palpitations due to thyroid issues, my trainer had me focusing on building up lmm to increase my metabolism to promote weight loss.
She focused on my my:
1) Back muscles (trapezius & lattisimus dorsi)
2) Butt muscles (guteus medius & maximus)
The exercises are pretty simple & for the most part, super popular. Rows, pull downs, (weighted) squats, etc.
I'm still pre-op (2 weeks left!) and will probably have to wait until mid-summer before I am getting enough nutrients in to start lifting again. I am by no means an expert, but my rearch leads me to suggest focusing on exercises that activate multiple muscle groups and keep moving up in weight. When I am weight lifting, I follow the rule of thumb that if I can do 12 of them without experiencing muscle fatigue, I'm on too low a weight. When I make adjustments to my resistance, I look for a weight where I struggled to get to 4-6 reps. Once I could make it to 8-10, I'd up the weight.
There are lots body building forums that talk about various rep/set methods (you can see a brief outline of some types here
). Experiment and see what works for you. Or you could cycle through them, since the body seems to respond well to change-ups!