I've used a thermal jersey with a long sleeved Icebreaker wool baselayer and maybe another short sleeve baselayer. I also have a tight fitting vest I can use. That works OK especially if you're working hard.

This year I've switched to a Castelli Gabba 2 jersey which is windproof and waterproof enough for a 1 hr ride if it starts to rain I use one or two layers of wool underneath.

I don't know if you're planning to buy multiple base layers or wash them every night but non-wool baselayers are more likely to stink than wool.