Hi Amy
We bought a nice memory foam type bed from Bensons in the UK a few months before we moved out here last September so we shipped ours with the rest of our stuff. I think we paid about 700GBP during a bank holiday sale for a UK King. The beds in our apt are brand new but not comfortable at all so we are glad we have it! We have Debenhams here so you can definitely find UK linen sizes. I wish I would have purchased a few extras from Ikea back home though.
Since our stuff took about 3 months to get here anyway, we had to buy a new duvet, pillows and linens anyway!