Based on the chart, it looks like you could use an X-small, or Small. If you are diving warm water with a 3mm bootie and thin sole, go with the X-small. For drysuit diving, or with 7mm booties, go with the bigger size. The good news is that they have a size guarantee as long as you don't take them in the water, so be sure to try them on (with the right booties & socks) as soon as you get them.
If it helps any, I wear a men's size 9 sneaker and use the Large fin with my drysuit in Monterey.
There probably is a spring strap, but honestly, I don't use them. I've logged 1200+ dives and worn out several pairs of fins (eventually you get a fatigue crack or the foot pocket starts to tear) but I've never had a fin strap break. (but I still keep a spare kicking around in case I lose one)
Spring straps were a great idea in the '70s, when rubber would get brittle and crack with age & sunlight exposure, but that doesn't really happen anymore. I know some tech divers swear by spring straps but don't let them bully you. I'm a PADI DM and trained tech diver. I routinely take these to 200' with the stock straps, wearing a drysuit and 5 different tanks. For a dive like that I worry about all kinds of things going wrong, but the straps never made me nervous...
My only quibble with the stock straps is that the outside buckle tends to catch on the kelp. My solution is tie the tail down to the strap along the outside of edge of each fin after the first time I set the strap length. Then I do all my length adjustments using the inside buckle on each foot.
Thank you for your response, it is helpful. the only reason why I was thinking spring straps was because I was struggling with the rubber straps last weekend. I'm diving in 42 degree water and am wearing thick gloves. The finger loops on the spring traps might be easier to get into. I borrowed a pair of fins from a friend two weeks ago that had spring straps, I liked the straps but not the fins.
I understand. I do photography in 40-ish water. It's tough to push those little buttons with thick gloves! As I said, I tie down the outside of the strap to keep kelp from catching, so basically I never though that side. Before I put them on I loosen the inside buckle all the way, that makes them easy to get on and I just have to tug the tail on the inside until they feel right. When I take them off I pop the inside buckle which gets the strap out of the way. It's just a habit now to loosen the strap all the way at the same time that I redo the buckle.
A trick I use for photography is to dress my head and body core very warmly. (I have a 12mm hood and wear several layers of REI thermals & sweatshirts under the drysuit) If you r head and core are truly warm, your body can afford to send blood to your hands & feet to keep them warm. With good peripheral circulation, you can get away with thinner gloves.
The Scubapro SeaWings have a bungee cord strap. They are genuinely strange fins, but I like them for recreational diving, especially when photographing big things like Manta Rays or if I might have to swim a long ways, or against a current. You might be able to adapt those.