I'm a trans woman with an intersex condition who came into the "fetish" if you can call it that, long after (several years after) starting transitioning. I didn't have much of a girlhood (or boyhood for that matter), and a pretty shitty adolescence. I tried my best to be as girly as possible growing up, but I was always hemmed in by what adults (not my parents, who were and are supportive) and peers.
While there is much in the "sissy" fetish I don't like, it's also a good place to start for picking and choosing between the aspects you like and don't like about ultra-femininity, submissiveness, etc. For the record, I pass, have passed for a long time because my intersex condition was a natural T-blocker to begin with, and am stealth is most cases. I'm not a crossdresser, and all my documents were changed over years ago. I just like that now as an adult I have choices that I didn't have as a kid. So I take what I want from the fetish and leave the rest.
As for whether transitioning is healthy, it was for me, both medically and mentally. My doctor also spoke about giving me artificial T if I wanted, but I've always identified as a girl, so more estrogen it was. I've been quite lucky to get very little pushback.