Hi! I know this is an old post, but since I'm new on the forum I just came across it.
Have you read any articles about making wool garments - including merino - less itchy? I've seen a bunch of them out there and it's a bit of a faff (soaking the garment in water with vinegar, then with conditioner, drying flat on towels, then putting in the freezer overnight), but there's a lot of articles saying the same thing and I heard from someone who tried it that it works...
I've had Helly (smelly) Hansen synthetic baselayers for years and I really liked them (an old model more than the one I bought more recently). I had the men's baselayer initially (I think when I got my first one they didn't do gendered baselayers) and found it fit great without clingy. For a better comparison, my dad has also used them for years and really likes them.
That said, I do prefer the non-synthetic base layers when I can get my hands on them. My problem with Icebreaker in particular is that I find they shred really easily (haven't bought anthing in the last few years, so maybe they have improved that?). I can't get merino easily in Peru, so I haven't tried any other brands.
I've heard that some people who find merino itchy, don't have the same issue with alpaca wool, but alpaca still shares merino's other benefits. I know it's not super common in the outdoor market (therefore hard to find and rather expensive!) but as far as I'm aware, there are a couple of companies out there that do alpaca wool base layers.