does anyone know where to get a coat/cover for a dog to keep the hair flat after grooming? It would be to keep the whole body covered?

Try this lady.  She's very helpful!
http://www.tradetraffic.co.uk/drydogcoats/

I've got them for my cavaliers as they have a tendency to sleep on their backs ;)

They work & I got them from here

you can order over the net or ring up & speak to the lady who makes them

The site tells you how to measure your dog

this is perfect, thankyou very much for the info, just what I am looking for :-)