If you are certain that psych is what you really want to do, I would apply broadly to categorical PGY-1 psych positions through ERAS and the Match, and try to get a position that way. Since you are a FMG, if a program really likes you, they could even sign you for a PGY-1 position outside the Match, if they really wanted to.
If you are not a very competitive applicant and are concerned about not matching into a PGY-1 psych spot at all, then I would simultaneously apply to prelim medicine spots as a backup, with the idea of transferring into a psych program later as a PGY-2.
If you really think you are not competitive enough to match into a PGY-1 psych spot, I wouldn't waste your time/money applying to transitional year programs, as they tend to be much more competitive.
Why do I advise that you really try and match into psychiatry as a PGY-1? Because our PGY-1 year includes 6 months of psychiatry (plus 4 months internal medicine and 2 months neurology). Those who enter psych at the PGY-2 level from other specialties start 6 months behind on their psych requirements. This generally translates into much less elective time for them so they can get the requirements done.
If psych is your passion, I think you are likely to get a much fuller educational experience by doing all 4 years of psych residency, IMHO. Just my 2 cents...take it for what it's worth.
