https://www.ncbi.nlm.nih.gov/pubmed/3219066 http://www.cakeworld.info/transsexualism/what-helps/srs http://www.cakeworld.info/transsexualism/what-helps/hormones http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2265.2009.03625.x/abstract;jsessionid=B762F82F4564FB01651D68B07C5AEEAB.f01t04?deniedAccessCustomisedMessage=&userIsAuthenticated=false http://www.sciencedirect.com/science/article/pii/S1158136006000491 http://www.tandfonline.com/doi/abs/10.1300/J082v51n03_04 http://bmcpublichealth.biomedcentral.com/articles/10.1186/s12889-015-1867-2 https://www.ncbi.nlm.nih.gov/pubmed/21937168 http://onlinelibrary.wiley.com/doi/10.1111/jsm.12155/abstract http://www.medscape.com/viewarticle/827713 https://www.erudit.org/fr/revues/ss/2013-v59-n1-ss0746/1017478ar/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3043071/
PDF http://www.scottishtrans.org/wp-content/uploads/2013/03/trans_mh_study.pdf
These two are about regret
https://www.ncbi.nlm.nih.gov/pubmed/15842032 https://www.ncbi.nlm.nih.gov/pubmed/24872188
These are some of the many many many studies showing reductions in suicide, depression, stress, and many many other areas including regret which is fairly low.
This includes some i didn't link.
http://transascity.org/quality-of-life-in-treated-transsexuals/ out of 34 studies reviewed, Most show improvements of some kind.