OP, Ergon grips with bar ends make a great improvement in comfort. They give you more hand positions. They make the bar end in multiple lengths, so you have some options.

I think most bullhorns are designed for road bar diameters, so your flat bar components may require some.... fergerstication to install.

Another option may be different flat bars. You can get a great many different rise and run angles, and my most comfortable flat bar was flat in one plane, 3° sweep in the other, and it was far more comfortable than the original riser bars.