I too had bladder issues, and began my HRT journey on topical oestrogen in the form of estriole, six months later I had a light post meno bleed, which led to me seeing a gynae at my local hospital for a hysteroscopy, she recommended Mirena coil, to protect uterus from any effects of the topical and any subsequent form of oestrogen I might need to use.
I had it fitted while I was there, no anaesthetic was offered, it was uncomfortable, but soon over.
I now use oestrogel and have an estring for vaginal/bladder issues, I also take one 5mg tablet of vesicare to help my bladder, recently I have been able to reduce that to every other day as bladder is much better than it was.
The coil did cause a bit of spotting for the first 5 months, but all fine now, and unaware it's there, if there is any progestogen in my system, it's constant and i can't say I notice, plus I have no bleeds, and apart from applying oestrogel every day, nothing else to think about.
Everyone has their own thoughts and opinions, at the end of the day, it's what works for you, and helps your symptoms best xx