How much more rise do you think that you need?

A riser bar won't give you much and it'll probably be wider so your back position won't be changed very much. Since the steerer tube has already been cut you can't add much (if any) spacer under the stem.

That leaves buying a higher angle stem. Picking the right stem is tricky because you have to consider the angle and extension together. If anything you'll probably want a longer extension than what you have now.