There are a lot of YTers that make custom order PJs. The site I would recommend is
www.mygofetch.com. Des is AMAZING and she has the cutest stuff.
Also, a lot of people use the SnuggleSafe Disk. It's a microwavable heating pad that stays warm for up to 12 hours. I haven't used it personally but I've heard lots of good things. You can buy all kinds of fleece covers for it.
Amazon.com: Pet Supply Imports - SnuggleSafe...
Hope this helps!