I'm almost your exact size - 5'2", 105lb. My first BC was Cressi Start Pro 2 in XXS - bought it and fit perfectly when I was ~100lb. Now it's quite snug and uncomfortable to put on/take off without using the quick release buckle (my shoulders/back are too wide after gaining some muscle). In other words I think XXS will be too small or at least be an annoyance if you gain any weight at all.
I searched for a travel BC that was as light or lighter than my XXS Cressi for a long time and couldn't find one I liked. I tried a backplate and wing for the first time last weekend and loved it. I have ~250 dives in my old jacket and it took me less than 1 pool dive (where I had access to an instructor to ask questions and fine-tune the harness fit) to get the hang of the backplate and wing. It is much more comfortable, you don't feel the tank at all, and easier to maintain trim due to where the weight pouches are (at the back near the tank vs in front). I used the Halcyon carbon fibre size small backplate - tried the standard and it was too big. Ordered that with a 20lb wing. Halcyon is expensive but I was told no other brand makes a backplate that small so that's what I went with.
I searched for a travel BC that was as light or lighter than my XXS Cressi for a long time and couldn't find one I liked. I tried a backplate and wing for the first time last weekend and loved it. I have ~250 dives in my old jacket and it took me less than 1 pool dive (where I had access to an instructor to ask questions and fine-tune the harness fit) to get the hang of the backplate and wing. It is much more comfortable, you don't feel the tank at all, and easier to maintain trim due to where the weight pouches are (at the back near the tank vs in front). I used the Halcyon carbon fibre size small backplate - tried the standard and it was too big. Ordered that with a 20lb wing. Halcyon is expensive but I was told no other brand makes a backplate that small so that's what I went with.