just get some anti-fatigue mats. home depot & lowes carry them now, as well as places like grainger & safety supply companies--even fisher carries them. at the home stores, they're sold in big square tiles, about 2 feet square more or less, that can be tiled together. all 3 of the darkrooms I use, have concrete floors. at home I use the tiles, at work--we bought the mats in big rolls, about 3 feet wide, and cut them out to fit in front of enlargers, sinks etc. the rolls are the best, the tiles are cheaper & easier to lay out, but they can accumulate dirt & scum in between....
btw--some of the mats have a slick surface & you can really bust your ass on these if they're wet--there are others that have a bit of tooth to them, grooves etc--and they come in all thicknesses too. first set of mats I had, got from Porter's of all places, dirt cheap too--they were factory seconds.
hope this helps