Hi Gzmo,
There is actually no such thing as a small claim, but anything under £5000 goes through the fast-track and is designed to require no input from lawyers. You can still start the process if it is more, or you can reduce the size of your claim.
Receipts are ideal, but anything can be used to prove ownership - bank statements, photos of the clothes being worn etc.
You are rights about New homes being excluded from most consumer legislation such as the
Sale of Goods Act 1979. However, you are still protected by common law and the requirement for a "duty of care" Have a look at this post:
Help/Advice needed please.
Trading standards will assist with court paperwork I believe.
Before you do this I would write them a letter stating what you are planning to do to give them the opportunity to resolve the situation before you start proceedings.
HTH
Tony