I've used this firm many, many times (although not for cushions - I'm usually ordering mugs) and I've always been highly impressed with their service and the quality of their products:
https://www.photobox.co.uk/shop/photo-gifts/photo-cushion
I ordered a personalised T-shirt from this firm earlier this year and, again, I was fully satisfied with both their quality and service:
https://www.smartphoto.co.uk/photo-gifts/photo-cushion
(You should note though that, despite the '.co.uk' web address, SmartPhoto is actually a Swedish firm and my T-shirt was printed in Belgium. So it might take a little longer for goods ordered with them to get to you when compared with those ordered through Photobox).
On the High Street, you'll find that the two Timpson-owned photo-processing businesses, Klick and Max Spielmann (which has a presence within many supermarkets), both offer the service you're seeking but that the products aren't produced in-store. (They have to order them from their central printing units). So you don't really gain anything from going to their premises.