layers is best - you might find you get warm in the morning when the sun comes out and warms up the tent . socks and hats are best bet, you lose a lot of heat from your head. eBay probably the best bet for DC pjs/warm things - don't just look for pjs, look for 'sports' type clothes, eg joggers or thermal/fleecy t-shirts.
The other thing I've seen suggested in other threads is to have a rubber or foil backed picnic rugs to put down under air beds - stops the damp making the air inside them cold, apparently.
In the colder months DS and I wear leggings and tracky bums on top of them, and fitted long-sleeved t-shirts or thermals with a hoodie or sweater. I have been known to wear four layers to sleep in sometimes, it is so cold.
Socks are a must, and I also recommend a buff (rather than a hat) to keep ears and head warm.