I am currently on my third engagement-wedding diamond ring. Long story. A couple of years ago we took my then current ring to a jeweler we like because the prongs had worn down and the Florentine surface had mostly worn off.
I had been looking at settings for a couple of years but couldn't find anything I liked. The jeweler helped us design a ring and found a couple of matching diamonds to enhance the original solitaire.
You will probably be wearing this ring for decades, so make sure you get something that fits in with your style, and not just because it's pretty or fashionable. For me, simpler endured and I still kind of miss my old style ring. New one is very pretty, but it's meant that some of my other rings worn on the right hand don't look quite right now.
And probably needless to say, decide on the diamond you want before you choose the setting. We had my old diamond appraised and I was surprised to learn that it isn't quite as good quality as the guy who sold it to us claimed. We didn't get an objective appraisal then, just took his word for it.
And yes, I always like a single stone setting. I have a round diamond, and did have a beautiful marquis cut in a right hand ring, but that was stolen by burglars.
Good luck. Do you prefer gold or white/gold silver for other jewelry you have? I always preferred gold until I let my hair go gray. Mixing and matching gold and silver is now just fine, but it doesn't alway work.