Not that it's overly relevant but Tredz is owned by Halfords, although it's not quite is the same bracket, but anyway, they certainly aren't the only places you can get bikes through C2W. There are a huge number of places that do C2W, so many in fact that you can pretty much get most bikes through the scheme.
Need to think about what kind of bike you want, as Pete says, Hybrid or mountain, but also bear in mind that availability is exceptionally low at the moment, with some manufacturers having apparently already sold out of 2021 bikes already, some quoting 12 month lead times, and some refusing to sell into the UK cos of the joys of Brexit. So your choice will be limited by availability, and if you want one "now", you'll probably have to compromise, and choose from what you can get your hands on. My bet is that the second hand market will surely be flooded shortly with barely used pandemic buys....