Some of my projects had needed better backgrounds than I had initially created and as there's nothing out there in Affinity Designer format I created the first background collection with more to come, you can't have too many backgrounds. Whilst you can use raster I like to stick to vector backgrounds for many reasons.
My first Affinity Designer background set contains 20 for your delectation. They're totally vector so, although they come in A3 size, they can be resized to suit and are easily modified for example changing the size of the floor and wall. They all have border and vignette layers, if you don't want them just hide them or alter them to your liking. Some also use conical gradients which you can play with to alter the effects by rotating, resizing and moving them. But make sure you do it on a copy it's easy to accidentally overwrite the original as we've all done at least once.
I'm leaving it up to you to add any textures you might want, there are tons of free ones out there, as the type and size depends on the subject, the scale etc.