I vote for the Jumbo! I am 5'1 and bought a Jumbo a few years ago. The Jumbo has that extra space that the medium doesn't have. The extra space is good on days when you need to bring a small umbrella, a notebook or LV agenda, a small makeup bag for long days and when you go day to night. It is larger than the medium, but still looks like a reasonable size on small frames. Also, the Jumbo will perfectly fall on your hip, whereas the medium will fall a bit lower or stay almost under your armpits. The jumbo will be useful on most occasions. The weight and chain are not that heavy. You can get used to the weight, if it is uncomfortable now.
I tried on the medium several times. It was a bag that I did consider a lot. I tried to see how I can fit all my essentials in there... It is a cute bag, but then there is a compromise between sunglasses or something else. You need to downsize. Anyway your bag will be packed and you would have to take things out to find essentials... the bag is pretty but will limit the occasions to use it. You already have a mini for those occasions, so the Jumbo gets my vote.