@shopsalot Good plan to ask before you buy. 🙂 Yes, there are a couple of good books, and the one I would suggest is 'Bonsai Basics' by Colin Lewis. Just right for someone starting out.
When it comes to buying a tree, one of the largest and most highly regarded bonsai retailers in the UK is Greenwood Bonsai Studio near Nottingham. They have a big nursery open to the public, and an online shop also. They also run beginners workshops.
There are many other websites and an overwhelming amount of information is online, but quite a lot of the info is not UK based, and doesn't necessarily reflect the needs of trees in our climate.
If you might be interested in visiting a show or event, there are a couple of really big national shows coming up soon, and as well as lots of trees on exhibit, there will also be many traders there selling trees too. If you look at the UK Bonsai Association website, there is an events guide and you can also join the association for free, and they give details of local clubs and societies too.
Hope that all helps, and yes, an outdoor tree would be preferable as they are easier to keep and most bonsai enthusiasts in the UK grow outdoor ones. The indoor varieties you find in garden centres and the like tend to be tropical species which are hard to look after, and have not always had optimal care before arriving in the store. The indoor ones are more like houseplants really.