Hi
@Judec77 I would source yourself a double seat and just pay someone to do the work for you. Make sure you keep the single captain seat yourself and don't leave it with the fitter.
Double seats second hand / nearly new are about £150/£250. Single captain seats are very rare and demand about £800 / £1000.
So may be better to pay someone to do the work rather than getting them to swap them over as they will sell on your single seat and pocket the profit.