A bristlenose wouldn't be recommended for your 10. They should be in a 30 at the absolute minimum since they are poop machines and need room to roam. - theres really no pleco that'd work out well in a 10 gallon
If you wanted to transplant a couple platies, you could get 3 oto's instead, they are schooling fish so you need 3 minimum, they are recommeneded for 20+ gallons, but 10 would work if you have a ton of algea. If you do buy them, make sure to go to the store around feeding time to make sure they will take algea wafers. None of mine will so I have to keep an algea farm growing in my tank at all time.
A couple amano shrimp could definitely work. I don't know what type of shrimp you had before, but these grow to a size big enough to not fit in your betta or platy's mouths.
Or you could go with some snails. mystery, ramshorn, or nerites. Nerites need brackish water to reproduce so are the least likely to over populate your tank. Apples/Mysteries have to lay their egg clutches above the water surface and need both a male and female snail so if you got unlucky enough to get one of each sex, you could still easily spot and smash their eggs. and Ramshorns are great little snails, they stay small and eat a ton of algea, but they also reproduce faster than bunnies. I got my first set of 13 in November and have had to sell off quite a few, quite a few times. Mysteries have got to be my favorite so far. They come in a ton of cool colors and get huge!
