Letters of Recommendations for a Transfer Applicant

[mellamomoma]

I am a first-year Ph.D. looking to transfer for personal reasons. I shared my reasoning with my current advisor, who 100% supports my decision and is also writing my letter of recommendation. My question: is there merit in getting two letters from my current institution (and the third one from a previous recommender) OR would one letter from my advisor (and two letters from previous recommenders) be sufficient in offsetting any red flags for the institutions that I'm applying to? I have another professor in my current program who'd be willing to write me a strong letter, but my only concern is that this professor has not known me for as long as my previous professors who wrote my LORs last year. 

Thank you. 

[al.pablo20]

If you don't mind me asking, what's the reason you're transferring? And how did you deal with the politics of letting your advisor know? I am a first year PhD student and I am quite unhappy in my department. I am considering transferring but I don't know how viable it is.