The latest tool in my garage is this B-G Racing mechanic’s kneeling mat.  I recently used it when I replaced a part under my dash. It saved me heaps of pain and more than a little frustration. Far better than one of those gardener’s mats, it folds out to a pretty good size. There’s also a smaller one, but I prefer the fold-out unit. When folded with the strap keeping it nice and tidy, it can be used as a seat. The foam is firm but comfortable. Whether folded or flat, it provides plenty of support. I bought it here from Mittler Brothers.