I completely understand and agree with you wanting to wear what you are comfortable with. I insisted on wearing a nightie for both of my labours (hospital wanted me in a hospital gown ) so I do get that. People say you won’t care, and towards the end that’s probably true, but at the start it’s not necessarily so. With my first it turned into a bit of a standoff with the hospital asking me to wear a gown, me asking if I had to, them saying I’d prefer it, me again asking if it was mandatory and eventually after them again saying it was a preference, me saying well no then, and wearing my nightie as planned.
However, I think you’ll probably have to concede on the pants long before that point if I’m honest. You will need to be examined several times during labour but it’s really not that easy to move around beyond a certain point so it’s not just a case of ‘I’ll just take my pants off when they want a look and then put them back on’. Even if you intend to have a very active labour, you shouldn’t underestimate the effect of having a giant head moving down your vagina will have on your mobility. It’s not just going to have an effect when they’re crowning, it’s long before then. Realistically I would expect that they’ll have to be gone from the point you start pushing, and also just for realistic expectations, I’d say that if they’re not off by that point then they’ll probably have to be cut off, as again I don’t think it would be tolerable to take them off yourself, so that then obviously prevents them from going back on anyway.
This is just my experience, maybe others will disagree, and absolutely no judgement for your desires at all, just trying to give you a bit of insight into what might be practically possible so you can manage your expectations.