Hm, this is a tough one to answer to be honest. It's completely fair and reasonable that prolapsing would be taken as too extreme by a partner, and honestly it shows that they care for you if they have such a concern. There certainly are risks associated with this kink so caution is reasonable. It also sounds like you two are already pretty in deep together kink wise, so you're not in an impossible situation to hash things out.
First, you must ask yourself what you truly want. Do you want a rose, or a prolapse? Are you willing to accept all benefits and risks? Once you're sure what you want, then discuss with your partner. If you are wanting to try and turn your partner around into letting your body do its own thing and what you want to do with it, here are a few points:
1. Here is the ultimate prolapse guide. It explains more points then I'll write here. It was written by @buskowianka12 who also has a twitter handle by the same name and has documented his goal of attempting the biggest prolapse possible. He isn't a great example to show your partner, because he is actually trying to make his prolapse as large as possible as his set goal. What you should do is talk about;
2. Prolapsing being a normal occurrence in many people that are into anal stretching, and to varying degrees. Lots of women doing anal these days have rosebuds through prolapses. To name a few you have girls like Jane Wilde who have small rosebuds, to girls like Siswet19 and Lexa Lite who have developed rosebuds going on prolapses from anal stretching, all the way up to the legends on this site such as Hotkinkyjo, Sindy Rose and Dirty Garden Girl who once again made it their goal to prolapse. Siswet and Lexa Lite among Roxy Raye and etc are better at showing that rosebuds are just part of the territory of anal stretching. Its what happens when you begin stretching the ring that hold things back, while also stretching the internal anal muscles and relaxing them too. With gravity at play, where is that tissue expected to be pulled out too?
3. The size of your prolapse also isn't entirely based on how far you can stretch either. Some stretchers never prolapse. Some people that don't stretch as wide as others also have developed significantly larger prolapses than others. Its also very much so a genetics and how your muscle ligaments in anal cavity are set up kind of thing. For some prolapsing is a breeze, for others they never achieve it.
4. Prolapsing doesn't have to be risky. I have repeatedly seen stars write about the effects their rosebuds and/or prolapses have had on their lives. Many people ask them, and they actually do respond quite often. Obviously I'm sure they have their own biases, but the common refrain is that they do not have any issues, but they have had some changes in their lives because of their prolapse. Buskowianka goes in depth about this in his guide, but common notes are:
A) No problems holding poop back. They still retain full muscle control over their sphincter, and feel their stretching/anal play has made their sphincter stronger (think a gymnast in flexibility). They claim to not have accidents of any sort. They also state that when they do go, its a lot easier for them to poo now, and don't have to strain anymore.
B. Related to that, they also don't prolapse unless they feel like prolapsing. Buskowianka has stated repeatedly that his doesn't come out unless he wants it to. One girl though, Melissawidexxx (A star with a goal of prolapsing) did write once though that she did accidentally let her prolapse go while doing yoga after running a half marathon.
C) The biggest risk of prolapse doesn't seem to be incontinence to me as much as more so in the more extreme prolapses, where it isn't a rose anymore and the tissue stays out of the body on its own and must be pushed in rather than retracting on its own, seems to be having it stay stuck out of your hole for too long of time. The problems here are the loss of blood flow which if gone unnoticed will result in dead tissue and surgery being required, or potentially being fatal. I haven't heard of this happening to anybody publically, but it is on the medical records as a possibility in prolapse patients. Then there's the risk of injury such as puncturing or infection from having internal tissues externally exposed.
D) There are a lot of unknowns worth considering too that haven't been touched upon. For example, I haven't seen any issues related to accidentally prolapsing in ones sleep, but its something I've wondered about.
Anyways, I hope that helped a bit. I'm sure others will have good suggestions too.
