I've never really worried too much about baselayers. i happened across some cheap Aldi merino tops and wear them because I have them and more recently have some cheapo Decathlon hiking t-shirts and running tops which are polyester and not so warm.
I see now the various brands have supposedly whiz-bang technologies like 2 layer (polypropylene inner with polyester outer) and "3D weave" blah blah
Seems t me that it mostly comes down to: merino (warm, absorbent, slow drying, doesn't stink), polyester (not as warm, absorbent, quicker drying, can smell), polypropylene (warm, not absorbent, quickest drying, stinks easily) - does that sound about right?
I'm thinking of the best thing to wear under Paramo might be polypropylene for it's non-absorbent nature but ability move water. But it would need to be thin or I'd overheat like I can in merino. I also don't fancy smelling like a rabbit hutch. In reality I've been fine with polyester in warmer weather and merino in colder weather but I've been clammy at times so always interested in maximising comfort.
Anyone got any experience or opinions on this?