I’m progesterone intolerant too and haven’t tried Slynd, but have tried Drovelis (which has the same progestin). However, the diuretic effect was bothering me (eczema flare up), so I switched. Mood wise, it was much better, it will also suppress your ovaries very well (first month was quite difficult for me), so you might not need the hysterectomy if you get on with it.
I switched to dienogest (also 4th generation progestin) + oestrogel, which seems to work well for me and might be even better for you if you have endometriosis. I’d say I’m still getting used to it, I’m now 7 weeks on it I think. I’d say my mood is slightly below baseline, but progesterone was horendous for me, so I’ll take slightly below baseline (it might get back to baseline, because I’ve read it takes 4 months to really get used to it. Even if it doesn’t, I’m happy I’m doing this well after 2 years of struggling). I think dienogest is also suppressing my cycle now, first month I could feel my ovaries waking up and I had some difficult weeks, but now everything starts to feel more level and side effects are getting much better (besides the acid reflux, but I’ve started on a PPI again).
However, since Slynd is in your guidelines (I’m in the Netherlands myself), I think it will be easiest to get prescribed and I recommend trying that first. Most people don’t have many problems with the diuretic effect, I was a bit unlucky I guess.