TSLA Men's Thermal Underwear Set, Microfiber Soft Fleece Lined Long Johns, Winter Warm Base Layer Top & Bottom

What size do i buy? Im 5'-9, 185, 32"waist, and typically wear medium bottoms and large tops.

What is the mhs100 and mhs103? Apparently you can order it either way and I don't know what it means or what the difference is.

what size would you suggest for 6'1" and 125 lbs, 29 waist? can't decide between small or medium. any suggestions?

do they have a fly