Not sure if this has been mentioned before but a good way to help keep warm when sat in a high seat is to have a piece of the insulated board (the type with the foil on) to sit on, each of the seats we have out have a piece tucked under the wood of the seat when not in use, when you want it just pulled it out and sit on it, you could even do the same to go behind you back.
This really makes a difference.
Hope this helps
Mick