There are many companies specialising in upholstery, don't know if you'll find any in the Isle of Wight though.
One I have used myself and was very happy with their service and the result was Regal furnishings https://www.regalfurnishings.co.uk/
bit of a way from you but they will allow overnight in their yard with hook up.
Perhaps an idea for you is to check out boat renovation companies, there are more than a few in your region, or simply Google motorhome upholstery.
Is the upholstery fabric or actual seating itself you are looking to change.
If itís just seat covers most are removable so you could possibly send all of your ďempty) covers off to an upholsterer so they can use them as a pattern? (Saves a long drive or expensive postage)
Its not the destination that matters.
It's who you share the journey with (even if like me, itís in a caravan!)
I am very fortunate to have Mrs Plodd to share mine with