I have often wondered what level of detail others like myself are able to fantasize at. I've found that as the years have gone by, I've been able to fantasize about much finer amounts of detail. Details such as the feeling of my hair on my back and shoulders, the look of my female legs as I point them in the air while lying on the bed, the feel of a bra and what my breasts would feel like supported in a bra, how would it feel to run my hands down the female curvature of my left and right sides, how a t shirt would feel to wear given my new proportions; the list goes on and on.
In fact, there are only two details I have had consistent trouble with. The lesser of those two details is what it would feel like to touch and run my fingers over the hairless female skin on my chin and above and below my lips. Whenever I try to imagine this, the unwelcome imagined sensation of stubble, and even the slightly rough sensation of shaved skin, overrides what I am trying to imagine.
The other detail is picking a female face, whether "stolen" from a celebrity or imagined as a sort of composite of desired female facial features and looking myself in the eyes with that face in the mirror. I always feel like either I'm looking at a blind spot, or a constantly-shifting collection of features which never stop changing for long enough for me to get a brief experience of what it might be like to see myself as a female in the mirror.