I would suggest picking the material you love. Use a reputable fabricator and tell them what you don't want. They can handle it. Post a pic and I can tell you exactly what I would do :)

Picture of countertops now in kitchen

Don't sweat that! That's no problem. A. The material will bend a little to conform to the wall. Yes, stone backsplash can bend a little. B. The splash can have a tight seam cut in it so it can angle against the wall. C. A little bit if caulk will go a long way in hiding the remaining gap, if any. Pick the countertop you love.

Remember, that backsplash has no give because it is attached to the countertop. The new countertop will come with splash installed separate. A lot more flexibility to get it to conform to the wall.

Thanks for the help. I really like the advice to pick what I love.