You can ask a solicitor to draw up a deed poll ~ not sure how much it costs nowadays but when I did it 9 years ago it was �50.
However the solicitor did tell me that I didn't need this document really..you can just say one day that you now wish to be known as Joe Bloggs and as long as you haven't done this for illegal purposes (escaping debt, fraud etc) it is perfectly ok. Mind you when I had to change my details at the bank they did want to see my deed poll document, so it was a good job I had it :o)
Mr P had his name changed by his mum to his stepfathers surname. All was well for years until he wanted to get married ~ as the name was different to his birth certificate he then changed it by deed poll..so this is the route I would recommend for you!
As for the name you choose, it is completely up to you. Maybe your mothers maiden name? or just pick a favourite out of a hat, LOL.