John Lewis shouldn't be any more expensive than Mothercare, or any other of the highstreet big chains. If they are, quote their "Never Knowingly Undersold" stuff to them and they should be giving it to you for the lower price.
"So, if you see or buy a product from us and find it cheaper with a high street competitor (that excludes online-only or mail order businesses such as Dixons, Amazon or Play.com, who dont have shops), as long as their service conditions are comparable, such as delivery charges and guarantee terms, then we´ll match that price for you when you buy, or refund the difference for up to 28 days afterwards if you´ve already purchased."... from Johnlewis.com
Plus, if you're at all unhappy with a purchase they will usuallly accept a full refund.
Boots or Tesco - both have lots of stuff that you will need at affordable prices. I love coming home to the UK to stock up on clothes from Tesco, especially popper vests (buggering expensive over here in comparison). M&S would be useful too, for underwear for you maybe?