Super Mario Boards

yes it is. furry conventions have fans dressed up as their characters in elaborate fursuits. also depending on what your oc wears, the job can be simple as finding appropriate clothes online to complex such as getting fabric, cutting out pieces, and sewing it yourself or embroidering designs yourself onto the fabric. you can additionally commission costumes to artists too, but they'll be expensive.

The OC I would want to cosplay as doesn't even really need an elaborate costume. Basically just a Shy Guy mask, some big black boots, and for my hair to be dyed.

then it's actually fairly simple, big black boots aren't hard to find online, you can request your hair to be dyed by a hair stylist (or get a wig if you don't want it long term). the shy guy mask though, what material do you plan on using for it?

I have no idea, but I'd like it to be solid. A friend of mine has one that's fabric and I know I wouldn't want that.

im not too knowledgeable on harder materials such as plastic but im sure you can find resources online that will help you get your wanted cosplay.