34B 5'8" Debating Silicon Mod 304cc or 286cc Under Muscle

I would go smaller if you're worried about being too big. You can always accentuate the small with push up bras and tight shirts, whereas if you're too big, you'll have to work to conceal them. Concealing them means wearing loose tops which then just makes you look bigger or matronly. I know this from experience. I'm same height as you, 34b, 133 lbs, and 8 got 360cc anatomicals, full height full projection. They were heavy, hard, and stuck out from my chest like torpedoes. I hated them and had them removed after two years. I revisited my PS and they are giving me a deal on a crescent lift (I breastfed) with inspira low profile rounds 260cc in right,290cc in left to correct assymetry. Im still worried about being too big and hard. But due to my bwd, they can't go down to the 170cc range like I wanted. The implant has to match the width of the breast , si to do that, I'm at 260cc. Im just hoping the lowest profile available will keep me looking natural and petite. Just my two cents on sizing.