What Else Can I Add?

[CommunityKepper]

Hi guys I have a 60l aquarium and in it I have 2 black widow tetras (I know that they are suposed to be in groups and but I have had these for years and did have more that unfortunately died and they seem happy) 3mollies and 3 platies and i was wondering what else would be suitable to add. I was thinking maybe a male guppy and was worried about fin nipping and would anything else be ok to add. Thanks.