Re: Is it possible to "make my own mat"?
Soft mats can be beneficial for practicing ukemi, the dojo I do most of my testing at used to have soft gushy mats. They were great for break falls, nice and slick for shiko. You can also compare soft mats to practicing in a giving material like sand.
Maybe try buying two sheets of canvas and stitching it up with sawdust inside. Or maybe a giant sheet of cork?