Well you only have two options if you’re intent on UV only. The thumb button or the hinge. Assuming it’s going to be used for hunting purposes the thumb button would be the better choice. There’s not any difference between the aluminum body or the stainless steel except for weight and color. Size wise the Medium will work for the majority of people out there. Wether you add the four finger to it is all personal preference.
I would suggest ordering the plastic mold from UV to see if you like the feel, then I would suggest trying to find one to sample before going all in. I was fortunate that there was some nice people at the archery range that let me try their button releases so I could compare my current release to the button. Allowed me to evaluate if the change was worth it such as any anchor point changes. I went from a whipper snapper to the button and the change wasn't very drastic for me. Main reason for my change was the customization I could do on the button that's not available on the whipper snapper.
Also be aware the length of the release neck on the UV is long. What i mean is if you look at the UV releases, the point where your hand holds the release to where the D loop attaches on the releases is a huge distance which may affect your draw length in order for you to anchor in the same location. For me it’s a substantial amount and adjusts my draw length by about 1 inch. I use a Carter Too Simple which has a really short neck. So depending on your anchor point and style the UV releases can cause a need to adjust your draw length shorter. It’s not a big deal but it is a factor.
I am using the UV button releases, got the SS model cause I liked the feel with the added weight. Very nice and easy to get used to. Tried some STAN releases first but for me the UV was better (or I liked it more)
What wrist strap release are you coming from? I came from a Scott Little Goose going back to when they came out on the market. Most recently have been working with several thumb releases and a hinge release. I ended up buying two new wrist releases to try which are the Scott S2 and a Stan SoleX. I actually enjoy the accuracy I am getting now with those two wrist releases. Their adjustments made the difference.