1st allow me to make an assumption...that you'll be sleeping in either a sleeping bag or under blankets. In both cases, you're normal body temperature is 98.6 degrees F. If that's the case..if you're very hot when you get in your bag...you'll be hotter. Then you'll sweat. Then you'll be uncomfortable! If you're cold, the opposite happens, you're core already cold...remains cold and in your bag...you're cold.
Confused...thought so.
Sleeping bags are most effective at retaining heat when there's little between your body and the bag. Therefore, if you're going to be both comfortable and warm, or cool...wear as little as possible when in your bag. For ladies, a pair of silk panties or shorts and a silk top are just fine. For guys...poly pro/cotton t-shirt and lose shorts work fine. If it gets a bit cold...put on a pair of liner socks...that will help a lot.
I suggest strongly against ever wearing the next days cloths in your bag...why, because while you sleep, your body oils permeate the cloth and you stink. Also, unless you're carrying several sets of walking gear, the stuff you'll wear tomorrow, you may have worn today..even if you washed it, the chances it's not dry. And your bag either gets dirty "inside" or wet. Both bad for your bag.
Now, some folks are sensitive and tend toward being embarrassed, or shy. My suggestion is...we've all seen it before and there's nothing to hide. That said, I don't think folks will go out of there way to make you uncomfortable...but after all, this is an albergue...not the Ritz.
Buen camino,
Arn