I'm not a "gelatin junkie" but I agree with Rick that ballistic gelatin gives us a repeatable standard by which to compare results. It doesn't translate perfectly to the real world but it is repeatable. So from a scientific point of view, it gives us a good method of comparison; that's all. It's a yardstick.
And as Rick correctly pointed out, the minimum depth of penetration standard is based on the fact that gunfights rarely occur with naked people facing you head on.
I will add that the goal is NOT to produce a beautifully mushroomed bullet. The goal is to stop the fight. Ammunition manufacturers have sold millions of rounds of self defense ammunition packaged in flashy boxes accompanied by lots of advertising with pictures of mushroomed bullets. I can promise you that if someone is trying to hurt you or someone you care for, you're not going to give a damn what the bullet looks like when it's over.
The first order of business is the cartridge must work in your gun. Any failures to feed and function are deal breakers.
The second order of business is the bullet must reliably penetrate deep enough to reach something important enough to stop the fight.
After achieving adequate penetration, bullet expansion can be the icing on the cake but it is secondary to penetration.
When dealing with smaller calibers and short barrels, adequate penetration is often difficult to reliably achieve.
One of the reason the European spec 32 ACP round was effective, even with a FMJ; was the relatively high velocity coupled with a small frontal area. More often than not, it would at least penetrate deep enough to get the job done..
Given the OP's limitations in components, I think he's on the right path. If possible, I would look for a powder that gives the highest velocity. Once that was achieved, I would adjust the alloy
If it were not for the current situation, I would suggest that he just go buy a couple of boxes of factory loaded SD ammo that had a proven track record. It's just easier. But these are not normal times.