walmart and various stores sell "compression shirts" and pants.
i bought my red compression shirt from walmart for like $13, brand is starter.
ive had my black pants for a while, they are for winter to keep your legs warm but they are skin tight. i plan on buying a matching red compression pants strictly for iron man suits.
champion brand at target sell BLUE compression shirts and pants, i plan on buying a set for the iron patriot suit.
you dont want loose clothing under a suit, it looks and feels groce.
and it binds up with hinges or tight jointed areas.
stick with "compression clothes"
also can be found at sporting good stores.