For reasons of economy I have worked latterly with Fuji X-Ray film type HR-U. This is available on eBay and is very economical compared with traditional sheet film from Kodak or Harman (Ilford).
The smallest convenient size for sale is 8″x10″ which can be easily cut down with a paper guillotine to four 4”x5” sheets to fit sheet film holders for a camera.
HR-U film is red insensitive so can be handled under a dim safelight. A typical exposure value might be ISO 200, depending on the colour of the illumination source.
Chemicals and other stuff
Preparing the paper and developer requires sourcing some less-than-everyday chemicals. For some of these I have suggested sources; for others, you’ll need to scour the Internet, or order them from various companies in China.