Saturn, I'm curious as to what your character's art style is like (for what kind of feel you're going for).
One technique might be an idea to search for CC0 images on the web. Either to trace them in a vector program and place raster textures within the shapes, or to cut them out in GIMP and create a collage from them. I'd be happy to give you a hand in tracking down CC0 images you're looking for.
The character in my pfp (assuming you mean them?) rn is meant to have a gothic feel, they're a character in a 1920s murder mystery project I'll likely never finish which is also what I'm looking for backgrounds for. I might take your advice on that, I feel those would work well paired with the sprite artwork.
Okay, here's what I could quickly find with free/cc0/fair-use/public-domain for 1920's style or gothic:
https://www.pexels.com/photo/shallow-focus-photo-of-black-wooden-open-door-at-th...
https://www.rawpixel.com/image/3289206/free-photo-image-window-arch-gothic-windo...
https://pixabay.com/photos/arch-gothic-architecture-building-899062/
https://pixabay.com/photos/arch-gothic-architecture-building-62929/
https://www.flickr.com/photos/132740829@N02/23678012302/
https://commons.wikimedia.org/wiki/File:Tombs_of_Emperor_Takakura_1920s.jpg
The website snappygoat.com seems to scan multiple sources. But you might need to search Pexels and/or Rawpixel directly.
A tip for legit copyright is the ability to see who actually made the content and a way to check their work. Even when attribution isn't required, it's helpful to keep record of where you obtained your media. In case someone tries to sue you, you have a paper trail defence. Especially if the person trying to sue you has no actual control over the material.
