Clove polyps are crazy simple (care is similar to your GSP) and they’re beautiful! Lots of different colors to choose from and they’re not incredibly expensive.
As mentioned, Duncan are really simple to care for and clownfish (if you have those) love them!
Check out Acan Lords and favia! Tons and tons of color options with those for a relatively low price as long as you don’t get crazy designer ones or anything. Dragon soul favia and spicy lemon favia are favorites of mine
Mushrooms!! They don’t need a whole lot of light and there are a lot that have very simple care. Rhodactis and discosoma (mushrooms with polka dots or just solid colored) are the easiest imo. Ricordea and yumas are also very very nice and pretty, not too much care required with them either!
A green toadstool would look excellent! Very easy to care for centerpiece softie
if your tank is at least 6 months old!!! BTAs! Bubble tip anemones are gorgeous, and easy to care for as long as your tank is mature enough and your parameters are stable. Rock flower anemones might be more your style though because they don’t really sting