Sana kalmasın!

Its up to you! Referring to making a decision. 

Is this correct, and does sound appopriate? Not rude or patronising?

Thank you so much

I´m not too sure but since no one else answered... I think it should be

Sana kalmış

Kalmak - (matter) to be entrusted to someone (for sth) to be left to someone by someone else

so literally - it seems the matter is entrusted in you

my attempt

karar sen kalmış

karar sizin

or

karar senin - the decision is yours