The way I deal with boat Upgrades in this mod is I pick the best boat available at the current start date of my career. Since I prefer to start in 1939 when the war begins (usually,) I want a boat that is capable from 1939 to the end of the war. This means that I either go with the type VIIB in the 7th flotilla, or the type IXB in the Kiel Training flotilla (usually the latter for me, since I'm more of a type IX guy
.)
On a different note, I released an update to my localization fixes sub-mod that fixes a few more issues. You can simply re-download the file, and it should be the newer version now. I mostly just changed some radio message texts, and changed mentions in the interface from ''submarine'' to "U-boat" or "boat." I also changed references from feet to meters, so when you hover over the crash dive button for example, it now says "Takes your U-boat to 75 meters of depth" instead of "takes your submarine to 160 feet of depth."