I'm new to this forum having only found it yesterday. I'm looking for a bit of advice and perhaps to hear other people's experiences.

I am chairperson of a small but national charity which supports families affected by a rare condition. I was one of the founding trustees in 2013 and have been chair since 2015 although realistically I have always done 90% of the work.
I now find myself feeling like I don't want to do this forever. However, walking away is not easy, I'm very proud of what we have made and I want to know that it will continue. I'm feeling like I should draw up a five year plan to address the sustainability of the charity and to manage my own exit. Even if I were perhaps to keep some sort of advisory role.

I have thought a lot about why I feel this way now and they are something like this;

1. I'm tired! I also run a business, have two kids and I'm at university part time. Yet somehow I still make time to do everything that comes with the charity including organising events for over 200 people at least once a year.
2. I'm fed up of being taken for granted. The other 4 trustees do very little (Treasurer is the exception as he is very diligent with the accounts).
3. When we founded the charity, my baby son was recently diagnosed and my need for a community was very real. He is now almost 18 and his condition is not the defining characteristic that it once was. Therefore I find that its not great for my mental health to be thinking so much about the time of diagnosis and carrying other people through that.
4. When we started, there was no support group in our community, now we are the establishment and newly diagnosed families have a ready-made community if they want it. Although that was our aim it seems to have taken away any goodwill that we used to have with new families because they don't know how it felt to not have community. (Is that mean? I don't want it to be)
5. I do a lot of emotional support with newly diagnosed families when they are in their moment of crisis and I'm proud to be there for them however that takes it out of me and then I may never hear from them again once their point of crisis is over. Which does not make me feel great.
6. I have built lots of really strong connections in the medical and research community and overseas community groups look to us as an example, I don't want to lose those connections.
7. I have one really important project which should come to an end in the next couple of years and I want to see through to the end.
8. I think I'm less of a people pleaser than I used to be, I've done a lot of work on myself and I used to just say yes to anything which isn't sustainable and has led to burnout. I do not want that to turn into resentment towards the charity so I want to start this process now in an open and honest way.
9. Im just not sure it brings me joy any more...

My question to people with more experience than me - how do I navigate this, how have you done it, how do I honour all of the hard work and how do I make the charity sustainable well after my tenure? (and how do I stay reasonable with the trustees should they wish to stay?)