@brownie I would say get the 16kg to make a pair, buy a second hand one, carry on doing that until you are doing the squat comfortably as it only takes a split second to damage something that will take time to heal. I find myself in similar situation where I feel comfortable with one weight in one exercise and higher/lighter weight for another exercise. My 2 cents .
@brownie Perhaps you can try a different squat variation? Put the KBs on your shoulders instead of holding them in the front rack. It makes it a bit more like a back squat.
@emm I have found that this squat variation makes it easier to keep going when I'm getting fatigued, and it's closer in feel to the traditional back squat.
@brownie Sounds like you just need more practice. You can always go the “Easy Strength” route for more time under the bells and scale in if 2 x 5 is too hard.
@brownie Could be any number of things, but they will all likely be solved by spending more time holding bells in the rack position, and getting stronger legs.
I'd check out some technique videos on the rack position/front squats just to make sure you're not missing a quick technique fix. Otherwise, if you can do a single front squat with the double 20s I'd just work on doing more and more of them. You could also do rack carries/march in place with the bells in the front rack to get more used to holding the weight on your front. Something about double bells out in front of you makes them feel a lot heavier than the nominal weight.
@brownie The more you do it, the easier it gets. I can’t back squat (it’s because of shoulder mobility), so I always front squat or goblet squat. My front squat under a barbell is better than my friends front squat, even though they can squat way heavier than me. Why? It’s a skill and different muscle set.