My suggestion would be to try not to think of a birth plan as 'the plan for how things could go that I don't want to get too attached to because what if it doesn't work out?' That's not the point of a birth plan. It's a care plan you establish with your midwives or doctors. It lays out your care needs and gives them information they need to manage your care so they don't have to bother you to ask 10,000 questions when you're in labour. It can also help your partner to make decisions if, god forbid, you weren't well enough to make those decisions for yourself.
I hate being interrupted in labour. I like to be left alone to get on with it. So I put everything in my birth plan about how I would be doing things and any specific wishes I had for my care, like what things I knew would help me for the midwives to do, my pain relief plans, how I wanted the 3rd stage managed, vitamin K, the fact that we didn't know what we were having and wanted to look ourselves (rather than having it be announced to us), what sort of breastfeeding support I wanted after, etc. It was incredibly helpful to have all that written down. The midwives just sat and read it quietly and then left me to it. They only interrupted me when they needed to clarify anything and were really respectful of our wishes. It made for a lovely, relaxing birth.
It's not a guarantee that things will 'go to plan' but that's not why you write one. Actually, I think what's most important to include is what you want done in terms of your care if things don't go to plan. I had a home birth with my first, but I spent a lot of time being very detailed about my wishes if I needed to transfer into hospital and c-section plans if I needed one. That way I could make a difficult situation as relaxed and stress-free as possible. It made a huge difference I think and I could also just get on with it and not be thinking in the moment about things I needed to remember to mention to them. The midwives shared it amongst the team at their staff meeting when I was 36 weeks so everyone knew me and knew what to expect if they were on call for me.
I personally used the NHS birth plan page as a guide and then just added in anything extra that mattered to me, like about not wanting to be told the sex, breastfeeding support, the relaxation techniques I would be using, etc.