Not a lot of great options, necessarily. Many Soundbars are NOT known for creating great sound. (Though, to be fair, I have heard some success stories.)
If you have some speakers you can try out, you could simply put a L/R main speaker under the TV, using what is known as "Phantom Center" (simply not activating the center channel in the AVR) and all sound will be reproduced using those two speakers.
That will likely upgrade your audio quality, possibly significantly.
If you were trying to build out a full Home Theater experience, the advice would be significantly different and more expensive.
However, for what it seems you are describing, I think trying to add two quality standmount/bookshelf style speakers could do the trick.
Perhaps you know somebody that could lend you a pair to "try out?"