Agree with the other guys, crypts and Echinodorus all the way for me too.
@Nautilus143 I'd go with Crypt Crispatula var. balansae (
Tropica) in the corner(s) as
@Wolf6 suggests and let it trail across the surface. I'd get rid of the S Repens and replace with lower level crypts too,
Tropica have a very nice Cryptocoryne Undulatus 'Red' in their 1-2 Grow pot range, which is good value as you get numerous plantlets in one pot - I got one recently and got about 6 separate plantlets out of it, and could likely have split them a little further too. That and maybe some Crypt Becketii Petchii (Tropica) will give you some nice contrasting shades.
To add a splash of colour check out Echinodirus Ozelot Red (
Tropica confusingly refer to the red variant as just Ozelot, and the green version as Ozelot 'Green') to replace the water sprite, and maybe
Echinodorus Purpurea which is beautifully coloured Echinodorus that stays smaller than most (ignore the Aqua Essentials image, its much more colourful in person than that), and would fit nicely in the middle between your rocks.
If you go this route, budget for some decent roots tabs to add before the plants (I like the Seachem ones), as they are all heavier root feeders.