I got Ground Effects merino wool base layers and highly recommend it. It could be any brand as long it is merino wool, my partner has a simply top from Aldi (cheap supermaket here in Europe) which she loves.

Best part is that it is warm even when wet, dries pretty fast and it does not stink after a sweaty ride like other fabric does. I love to wear it under my cycling tops or fleeces etc as an extra layer. Keeps you nice and warm and wicks very well.

And it is great to wear while sleeping in your tent on a colder night, it will keep you nice and toasty. And will keep you warm if you need to do a call of nature in the middle of the night and it will warm you up fast when you call back into your sleeping bag.

http://www.woollypigs.com/2010/05/ground-effect-submerino-and-hot-toddy-merino-wool-base-layer/

Icebreaker is a quality brand. I've recently bought two items online. A fairly lightweight thermal long sleeved base and a pair of  running shorts.

I must say that buying clothes online is not the same as buying them from the shop so if you can find an icebreaker in a shop before you buy it online so you know exactly what you are getting.

I am not complaining but neither are quite what i expected.

once before i bought a base layer from wiggle online. I was disappointed with that because a) it was shorter than i thought it would be  (on the basis of the diagram) and b) it had moth larvae in it and so i've been getting holes in it ever since. Also its a bit scratchy which surprises me for superfine merino.