In the US there is an upgrade program where they will pick up your old bike when they deliver the bike+ and they'll give you $700 plus a mat, resistance bands and some yoga equipment. I would expect they have something similar in the UK. You could contact Peloton to find out.
In the US, people seem to be getting at least twice that and often more if they sell the bike instead so that would probably be more economical if you don't mind the hassle.
I'm thinking about upgrading as well
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