I would not add any more to your tank unless it were shrimp or a Nerite snail (just 1). Not just spacial issues but also temperment issues. I had my sorority and I had Neon Tetras in it (33 gallon tank with 9 girls at that point and 7 Neons) and the Neons became rowdy within themselves, they would leave the girls alone though. But because they were so rowdy with bickering among themselves and sparring, this actually really stressed out my girls and I ended up having to remove them.
But since you have a 10 gallon with five females, you could add up to three more females but if the girls are happy where they are without much fighting or bullying going on, I would leave it as is so you don't disrupt everything and potentially cause a disaster as I did. You could potentially add a trio of Otocinclus but you will have to have ample filtration for that to happen so they don't overrun your tank with their vast ammonia that they produce; all algae eaters are messy messy fish that just poop all the time lol. So you'll just have to do some extra tank cleanings to keep it nice nice ^_^
Shrimp wouldn't be too bad as long as your girls don't take them as snacks lol. I would try some ghost shrimp first to see if they are compatible and then move on if you wanted different shrimps like Cherries, if your girls don't eat them