I would be much happier with a female body.
There is something paradoxical, contradictory, about this that might repay analysis, I think.
I suggest the difficulty with 'I would be much happier with a female body' is not do with its truth or falsity, but rather with making sense of it.
The thing is, my (sexed) body (and think of this as changing over a lifetime) is not a contingent part of what makes me who I am; rather it is an essential part of what makes me, me. (Likewise, mutatis mutandis, for what makes you, you, I claim, in case that is not obvious.)
This is rather like when people say things like, 'Suppose I were to wake up tomorrow in a female body ...'. ... This is a strange thing to say because supposing I am a man whoever it is who wakes up tomorrow with a female body, it will not be me. Why? because my (male) body is essential to who I am.
[Notice the qualification, 'changing over a lifetime'. This is important. I could, for instance, have an operation that changes my body in a significant way. Or (which has happpened) my body could deteriorate over time. Talk of 'my body' in the sense I intend includes my body before and after such a change -- the body through change, if you like, rather than in a snapshot of its lifetime.]
So for me, a man, to have a female body, is impossible. Not physically or scientifically/technologically impossible, but conceptually impossible.
If it were a matter of inadequate technology, then of course things might change; what is now scientifically possible may change in future.
Could what is conceptually possible likewise change? Not in any useful way. Suppose the concepts change (note the plural here -- concepts intermingle, so changing one changes many); then, indeed, we might make sense of these new concepts. But, once we change concepts in this way, we will not be talking of the same thing at all. Changing concepts amounts to no more or less than changing the subject.
[This latter point is largely why people find matters so difficult when asked to say what they mean by 'woman' in wokespeak, I suspect.]
The mistake here is not obvious, I think. It is basically the same mistake the philosopher John Locke made in his famous example of the prince and the cobbler (see Locke, Essay, II, xxvii, 15). Locke wrote in Descartes' shadow, of course, and the connection between the Cartesian ego/soul and the idea of gender identity is an obvious one to make.
[An aside re souls. Christian theologians, faced with reconciling the essentially embodied nature of humans with the wish to make sense of eternality, came up with the idea of 'the resurrection of the body'. Why so? -- Because without my body, it would not be me there in heaven, since my body is essential to me being who I am. A disembodied soul? Not me, in any real sense. Neat, hein? (Not that christian theology particularly makes sense as a whole, but, well, there you are anyway; they try.)]
The error, like many common conceptual mistakes, is in a sense a deep one. I am not sure everyone reading this will understand. But, a plea: if you feel like saying seriously something like ' I would be much happier with a female body ', please consider the possibility that you may be making a mistake in how you think of these matters.
[One last thing. Thinking of Locke reminds me of the notion of 'identity'. His prince/pauper thought experiment was to do with personal identity -- with exactly this 'what makes me, me'. Why 'identity', though? Well, what makes me, me is what makes me the same as I was in earlier times.
What makes me the same person I was sixty years ago? See remarks about 'changing over a lifetime' above; what stays the same through change? That is me. 'The same' here is my 'identity': that (whatever it is) which makes me the same man/person (Locke distinguishes, but never mind) as changes happen over time. I suspect present-day debates about 'identity' might usefully be clarified if the notion of personal identity were considered together with the relation of identity ('same as') as in Locke. Just a thought.]
(Turned out a bit long, that. I hope it is relevant to some of the thread, though.)