You could buy gift cards with your debit card, pay for the majority of the price with that, and the remaining couple of quid with a credit card. The only thing to bear in mind is that if you changed your mind and wanted to return the item, the refund would go to the original payment methods.
I’ve done this before when buying things like appliances, and was able to get discounted gift cards through an employee benefit site, but still wanted to get the S75 protection.