Hello and welcome
I think some small catfish, a pair of Apistogramma and a school of cardinal tetras would look nice Tiger barbs can be quite aggressive from what I've read, and also aren't particulary colourful either. Cardinal tetras are peaceful and also look gorgeous, and you don't see any ugly mutations at the shops either, just the natural coloured fish
I definately recommend Apistogramma, they are so cool and full of character and are easy and fun to look after :happy2: Wild kribensis (Pelvicachromis taeniatus) are also another option, which are also beautiful and are much more different to the normal kribs, if you are looking for something more unusual.