Most packages require a BT landline which will cost £10 or so each month plus something for connecting it. If you've got this, you can start with a 1 month contract (plenty listed if you use the green "broadband" tab at the top).
If you already have other services and can get broadband for only £5 extra, that would be hard to beat.
2GB monthly usage is likely to be enough if you don't watch videos or listen to the radio on line. I had an "unlimited" service and only used about 1GB, then I switched to a 3GB limit and, if the others get going on the computer, it now gets close to that each month. My advice is to sign up for a 1 month contract so that you can see what the limits mean to you. The "download speed" figure means nothing. Some providers give a good connection, some don't, but the "download speed" figure is irrelevant.
If you sign up to a contract online or over the phone, you can cancel without penalty under the distance selling regulations within 7 days if the service isn't up to expectations.