I would get a cashmere blend Kiwi Pie. They are a nice balance between being trim enough for daytime (though not super trim or anything) and working well for overnight. Plus, they fit well over every single diaper in DD's extensive stash.
I know they are not exactly easy to get, but she has been doing larger stockings lately, so they are easier than some and they show up new fairly often on the TP.
For easy to get wool, I actually love my Nikky wool cover (yes, just the basic velcro, available everywhere one).