Hi Morbidia. Well, don't really think that I can advise on the content of the ritual - coming from someone who is not at that stage of my life or been through that passage it wouldn't be particularly clever of me

However, I notice you're in the South West. How far are you from Cardiff? There's a site there: Tinkinswood, that is a very old woman indeed and she would welcome you. I suggest a full moon and a trial run beforehand so you know where you're going. Walk out there by yourself and you'll see the moon come right up between her legs lol. Sit on top of the cap stone and just spend some time with her. I've had a number of profound experiences there and I know instinctively she'd be a good place to go. Though wrap up warm if you go in winter. When you're finished there, when you've had the thoughts you needed to have and you've talked with her long enough, go down inside her and there's a small hole on the back right you can crawl through - like a little re-birthing

May need to paddle to get there, sometimes she's watery lol
Rites of passage often have two parts: the lone part, in which you need time and space alone to consider the change and to make the change, and also the group: the community and the people who have been there before you. If you have close friends or family who have been through that transition, that's a good time to get together for a meal and a laugh - listen to their experiences. Let them support you through yours.
The problem with this transition is that culture as a whole is changing. There are three facades that need reconciling in my mind’s eye, different ways of looking at elder women in society:
1. As an elder, as someone wiser and life experienced. Something recognised in Pagan society and in ancient cultures perhaps, but not valued in wider society.
2. The Victorian 'out to pasture' attitude towards women passed child bearing age. The overall attitude to women that stifled the holistic view of life experienced wise women. You have to reconcile your place in society with society's view of you - you have to have a strong answer to both. To know where you stand; where you're rooted.
3. The modern-age view of women working and being entrepreneurial and socially active well into their old age - far beyond the expectations of women in times gone by: that you can be healthy, active, income-generating and independent for a long, long time. An active elder in a way women haven't been before, or in cultural memory. A new freedom.
So three areas to think about perhaps. I know the
Brahma Kumaris offer rites of passage workshops and workshops focusing on the role of women throughout their lives. Perhaps worth asking your local centre if they do anything - it's run by women so they might be good to just talk to.
Let us know how it goes, perhaps your experiences and what you decide to do will be useful to others wondering the same questions.