What sort of bottom-feeder would best suit a 10 gal containing 2 smallish goldfish (2-3 inches)?

I actually don't recommend adding any other animals with your goldfish. Goldfish tend to pick on other fish or get picked on themselves. Many people keep plecos with their goldfish. I have one with my three small fantails in a 65 gallon tank. My pleco is 15" long and over a decade old. Common plecos are simply too large for a 10 gallon tank. Plecos of any sort may suck on goldfish, normally when it's a small pleco with larger goldfish. My pleco is too big to do that. Aside from plecos, someone might suggest, as far as bottom feeding fish goes, corydoras catfish. I had panda cories with my goldfish a decade ago. One day after a year of harmony, I caught a cory eating a sick fantail's fins so that was the end of that.

Looking past fish, I might suggest a snail. Apple snails grow large, sometimes baseball-sized so a 10 gallon is too small for them eventually. Trapdoor snails are a better bet. Goldfish sometimes eat the antennae of snails though.

My goldfish themselves have grown to 12 to 14 inches for single-tailed goldfish and half as large for fancy goldfish. So, your two goldfish should eventually have a tank over 20 gallons if at all possible. They will do just fine without other fish or bottom feeders or algae eaters in the tank with them.