Build in one go and print in place design, 608 bearing weighted door closer. Add weight to your specific door yourself (i used screws for weights in my photo. Doesn't fully shut your door (pets can still access by pushing) but keeps it held near enough closed each time you use it.
UPDATE: I've recently added a dog handle so your pets can learn to let themselves out without you having to keep getting up to do it. WARNING if windows are open there's still potential for your door to slam, so please be aware of high winds and slamming doors. As it's easy to open your pets can pull on the pet handle and let themselves out as door stays slightly ajar.
V2. Door frame bracket is slightly larger to fit the 608 bearings tighter/better. V3. Better main bracket design for print in place and added hole to dog handle for attaching rope for dogs to pull open.
Settings that work well.
Wall line count: 3-4 Top/bottom layers: 3-4 Infill: 25% Concentric infill: on Supports: off