Woollen shorties/longies

Hi!

I've never used woollen shorties or longies before and was considering them for winter. If you have used them can you please give me some info?
Do they go straight over a fitted nappy, such as a bitti boo? With no PUL cover as well?? And they don't leak/get wet?
I'm a terrible knitter, but thought if I started now I might get some finished before winter...
Do they need to be lanolised before use? Or just after they've been used a few times?

TIA!