A contract is best, there’s usually a get out clause as well. If you’re not happy at all just have a word and give them 2 months notice. If you’ve got a contract and a good deposit (6 or 8 weeks) they’ll be more than happy to comply.
As for expenses – new furniture, stuff for decorating, tools etc. I think you can even get a kitchen/bathroom done as well. All this can be classed as reasonable expenses – sadly a new full susser can’t :-)
McHamishs post is an eye opener – just make sure you get as much information as you can about them and start within your circles of friends.
Good luck