I think a helpful way to approach it is to start out with the mindset that there is a time and a place for every intervention in labour, whether we're talking emergency c-section under general anaesthetic or gas and air or candles or birth pools or episiotomy or induction. These are all useful things in different circumstances and it's simply a case of judging, partly by yourself, a huge part by the professionals supporting you, if and when a particuar tool will be needed. Women labour at different speeds and intensties. Your energy and hormone levels will not be the same as someone else. Your baby's position might be different. An emergency might occur. Particularly for your first baby, it's somewhat of an unknown quantity.
Nobody wants to have a crash section under general, but if the choice is that or one of you dying, obviously you'd choose the surgery every time. And while you might prefer not to be induced, if it comes up it's likely to be for a legitimate medical reason and you can ask why.
You can always ask about the risks, benefits, alternatives of any option you're being offered - if it's really life or death then obviously you won't be consulted, but they should debrief you afterwards so that you understand why the decision was made as it was. If this does not happen for whatever reason, you can absolutely request it and I believe it's a simple procedure to do so for up to six months after the birth.
Don't assume that you can "choose" a drug free, intervention free labour because you simply do not know what the circumstances will be. I think when women are sold a birth plan under these assumptions then you end up with the disappointment and feelings of failure, which is a huge shame as it can be such a positive tool.
So with your mindset about all interventions being useful in some way even though no intervention or coping method will be appropriate for every single birth, you can write your plan. I recommend being concise, and splitting into three sections. In the first section you include information about you which might be different from the norm, important for your caregivers to know or just useful during labour. For example, you could include any known allergies to drugs here (although they should be in your notes too) but also things like "I struggle to focus on sound if there is background noise" "It's OK to tell me directly what to do" "I have a fear of needles and would rather you don't tell me if you're about to cut/inject (etc)" "Due to an experience of sexual assault, it is very important that you ask me before examining me" - whatever works for you.
Second should be your preferences section. I'd include in this anything that it's fairly likely you'll have control over no matter what else goes on - for example, whether you consent to vitamin K at birth for your baby and which method (Injection or oral), whether you want active or physiological management of the placenta, whether you want to discover your baby's sex for yourself, want the baby to be towelled off/wrapped/left vernixy for your skin to skin.
Third should be an If....Then.... section, with specific requests for what to do (if possible) in certain scenarios. For example I always put that if the baby needs to go somewhere I can't follow, I absolutely want my partner there instead, and I'm happy for him to prioritise baby over me. (The baby, incidentally, does not know or care, so it's not wrong if your preference is different here :))
Keep each section to max about 6 items, so that it's short and punchy and easy to remember. This way your caregivers are likely to actually read it, not laugh at it (they will probably say it is more useful than a standard birth plan) and be able to implement it because it is clear and easy to remember. Don't include things like "I don't want to be induced/cut/have pain relief unless medically necessary" - those are things that first of all are probably already NHS policy, so you don't need to request them specifically, but also are things you will most likely be totally calm and not actually in a compromised state when they want to discuss with you, so you will be able to discuss it and decide based on their reasoning and your feelings at the time. If you know you want something very specific like an epidural ASAP or the use of a birth pool, put that in but if you're happy to go with the flow for pain relief and try what is available and see how you go, then just do it - there is no need to write that as that will be their approach anyway.
It can be worth having a separate sheet specifically for your birth partner(s) to refer to which lists ideas that you think will be particularly calming or helpful during labour, perhaps things you've read about or practised in antenatal classes.
Lastly, I don't think this is a thing in the UK because I don't remember it - but in Germany where I had my second, it's possible to make an appointment with the hospital and pre-fill-in all of the consent forms for things like epidural, c-section etc just in case you need them later so that you don't have to try and roar answers to questions you don't know through contractions when you just want them to get on and do it. So if that is possible, I highly recommend it, obviously giving consent doesn't mean you'll definitely have those things, but it means if you do need them you can skip that one step.