Stocking for an 8 gallon Bioorb tank

[Eden]

I have a dumbo betta in an 8 gallon. My roommate and I want a Nano fish that isn’t better looking than our betta, and will not clash with the colors in the tank. Here is the picture of the tank. Please help.

Also, because the tank has a filter that is at the bottom under water, I am not allowed to use sand. I have rough rocks, designed to have a lot of surface area for bacteria, at the bottom. I have smooth river rock as a layer on top to protect my betta’s fins. I know I can’t have corys, but is there another nano bottom dweller I could get, or only snails? 
 

Again, if I can only get mid water nano fish then That’s what I’m looking for. 
 

Thanks,

-Eden

[Jollypop4321]

Very cool orb

[RovingGinger]

They’re not a fish but what about an amano shrimp to help clean? That or a big mystery snail would be cool. I don’t know all the fish options but I’m struggling to come up with something that would be happy on its own and wouldn’t be an issue with the betta, for that tank size. If it were me I guess I’d try some guppy fry I wasn’t very attached to. 

[Eden]

Thank you @Jollypop4321 and @RovingGinger

Can guppies manage the higher temperatures with a betta?  

I was thinking rice fish maybe?  

The only thing left would be chili rasboras or CPD, but my roommate doesn't think the red or orange will go with the colors we have.  

[Eden]

I don't want colors to clash, and we don't want the fish to be more gorgeous than Dart.