You have done well to manage the situation for ten years. As you have found with severe prolapse many pessaries do not stay in place, are uncomfortable or cause bladder and bowel dysfunction. I also envisage that irreversible colpocleisis must be a big decision for you at this time of life especially as it can also bring with it the attendant issues of bladder and bowel problems.
So many women report that pessaries do not stay in place, they are uncomfortable or cause similar issues as above.
There are 'space saving pessaries' on the market, that purport to occupy the space in the vagina which will hold back the bulk from prolapsing through the vagina but seemingly they are not prescribed by the NHS and do carry their own problems.
To replicate the space saving method in the UK the NHS can use two ring pessaries which gives much stronger support. I would urge you to speak to your GP or gynaecologist about this method before making a decision about surgery.
You can start with the smallest of sizes 50mm fitted in first then 53mm fitted in last. These sizes can be incrementally increased slowly and range upward from 56, 59. 62, 65, 68, 71, 74, 77, 80, 85, 90, 95, 100mm.
It does mean a further trial in what must be a tedious process for you but it puts you in more control rather than others guessing and estimating the size and type of pessary and could help avoid risks of anaesthetic/surgery if it works. And will better allow you to make an informed decision about surgery if it doesn't suit you.
It should be noted by those advocating a hysterectomy that this may temporarily resolve the problem for some but it is also is a contributing risk factor for further pelvic organ prolapse and urinary incontinence later due to pelvic floor weakness of abdominal supports and nerve supply over time.
I wish you all the best in whatever decision you come to, I can be messaged privately