But Under Armour isn't a "surf" brand... I couldn't possibly work
I will wear nylon/lycra compression shorts under my 3/2, 4/3, or 6/5 (like I ever take THAT out!) to keep the boys a little more insulated, which mainly means prevention of the frostbite-like effect when you piss body temp fluid while submerged in sub-55 degree water.
I have 3mm neoprene compression shorts (much harder to find, but out there) that I will wear under baggies when the water gets 56+ and air is 75+ because I just have an aversion to clothing at all and progressively shed the neoprene suits in descending thickness two steps ahead of normal temp chart guidelines as the water and air get warmer. I wear that combo with a 2mm topper (drylock XCEL is great) or a LS or SS nylon/lycra rash guard top if water is 62+ and air is anywhere from summery to warm. Cant wait til it's Africa hot and I go shirtless lathered in petroleum jelly and a 1mm neoprene loincloth.
Really though, all of that was true except the last one which I can't say won't happen.
My head doesn't get cold, nor does my core. My nuts, feet, and hands get cold in order from most to least. Shed the gloves at 56+, down to 1.5mm reef boots at 58+, then free balling at 66+. Til I realize I may not have kids if I keep that up.
This for the past two years. I also have two pairs of wetsuit shorts. I think they are rip curl that used to wear under my shorts at almost all times. The UA shorts are a bit thinner and more comfortable in the summer. The only problem with the UA was at the beginning they were so slick that sitting on my board my butt would slide around between the UA shorts and my boardshorts. Once they were worn in a few times they weren't as slick and I didn't slide as much.