How to make a rubber cover for the hammer

I have a hammer (wooden handle with steel head) that I love (kind of an heirloom) and I like using it for lots of things. Its great for most jobs, but there are some things where I don't want the steel hammer head to make contact with what I am hammering. Instead of going out and buying a separate rubber hammer, I want to create a DIY hammer accessory whereby I slide on a rubber sleeve or cover on to the head. This way, whenever I encounter the kind of tasks that require a rubber hammering end, I can just put the rubber cover on and hammer away.

The trouble is, I'm skeptical as to how feasible this idea is. I haven't seen many rubber products out there that are close to being the right dimensions to fit snugly on my hammer. For example, I found some hammer covers on amazon but they are actually whole rubber head replacements and they interface with a screw threading. I just want a slide on cover.

Then I thought, maybe I can call up a rubber manufacturer and say: "hey uh, want to help a brother out?" but I think that's most likely going to be a difficult course of action because I don't know any one who works in that industry and I have a sinking feeling if I want a custom mold they will need a minimum order (like 1000 pcs or something).

Here is a visual representation of what I'm after:

EDIT My hammer is pretty much like this picture, wooden handle and everything. One difference is that my hammer head is actually a square, 1.25"x1.25" Depth doesn't matter so much, but I'd want the rubber cove to probably be around the .25-.5" range. Sorry for not providing this information earlier; just realized how important it was 🙁

Question: Is there an economical way I can tackle my thus far hypothetical DIY rubber hammer cover project? Or alternatively, is there a product out there somewhere that could work for my task?

Further Clarifications:

• rubber cover must slide on snuggly to my hammer
• ideally, for DIY approach, I'd like it to fit perfectly (tailor made feel) if that's possible
• budget is $20
• must work with my heirloom hammer (no buying other rubber hammers as replacement)