THANK YOU for this thread and recommendations!
I'd been trying for so long to find a cheap way to set an un-calibrated-size stone. I took the plunge to contact natcha_creations and it couldn't have gone better. The level of service, communication, and attention to detail was so beyond my expectations. I just asked for a 1mm change to an existing setting of theirs, and they added little gallery details for extra stability without my even asking, they sent CADs for approval (!!) again without my asking... just awesome service and makes me feel confident trusting them with any level of project. I did have a question because the measurements on the CADs were 0.2mm off from my stone, but they said that was normal and not to worry, so I gave them the OK. Well it fits perfectly! I got a halo setting and was trying not to have any expectations about the stone sitting high vs low - thankfully it looks great!
I don't have any jewelry tools, but a needle-nose pliers from my hardware kit worked to get the prongs secure and ok-looking from straight-on. They're not flush to the stone as I'd like, but I think probably "the perfect is the enemy of the good" at this point, until I have more practice at this, haha.
Stone is a 3.57ct electric blue topaz: