As long as both boobs have dropped it should be fine for u to get measured.
The boobs need to have dropped into the pocket made by the surgeon so they can actually fit into a bra cup. I had an issue where one hadn’t fully dropped at six weeks and was about a cm or two above where the dropped boob was, I saw my surgeon for my check up and she said to wait (to get measured etc) the nurse said the same too.
U may find it uncomfortable at first with a wired bra as they can dig a bit. I only wear mine to to work. I went braless at about 3-4months post op and generally wear non wired /Crop tops on weekends or go braless on a night out. I wouldn’t advise going braless at six weeks as its still early days and fluffing will need supporting.
There is no harm in getting measured it may give u an idea of what style of bra u want. Try a few places also as each store may measure different.