I have a couple of Odlo tight-fitting long-sleeved baselayers, after reading various reviews and tests I bought two on a special offer. I'm normally a medium but decided to buy the large versions and I'm glad I did, the large feels fine as a size but overall I'm disappointed with them. I've learned from experience that I'm just not a fan of having that 'trussed up' feeling, they cling all over, including my arms and they always seem to have a hard-to-describe chilliness about them which never seems to go away. It could be that they are working well but I just can't deal with the 'chilly' sensation for more than about an hour. I now use them for running only.
So I'm on the lookout for lightweight repacements, I'm also looking at the possibility of merino wool as well. Merino for me, has always presented me with a problem. I already have one merino baselayer (a cheap one) and every time, until the end of last year, that I wore it, I started to itch, especially when I was walking up steep hills and I always itched badly across my chest area. My wife thought it might be the detergent that we use so we've changed and it seems to have made a difference. The best one so far seems to be Persil normal. I'll test it more in the next couple of weeks by wearing it when I run to see what happens. As a side note, I can only use aluminium free underarm products, if I don't I itch like crazy! Maybe there's a link and I'm just an oddity?