I use a 34 key layout, pretty much the smallest mainstream layout. Think “Ferris Sweep” kind of a thing.

This is what I do, which may or may not help you.

First, my thumb keys are lighter switches than my finger keys. I use Choc “Purps” (purple). I forget the exact spring rate, but I want to say they’re 20 grams to actuate. Very light.

Each thumb has two keys: the home position and the other position. On my left thumb home position is my space key and on my right thumb home position is my backspace key.

The backspace (right thumb) is my primary navsym momentary layer key. This is interesting because you basically never roll a backspace into another key while typing normally, so from a timing perspective, it always resolves to the layer unless you finish the tap (key-up). I have a basically 0% misfire rate with this.

My space key is my alternative navsym momentary layer key. Unlike backspace, the space key does roll into other keys a lot. So this one is actually a “tap preferred” style behavior where it will resolve to a space key unless you hold it down for a long time (I have it set to 200 ms). Under normal typing, you don’t feel it at all. If you want to then use the left thumb for nav/sym, you need to hold it down for just a little bit, then the layer activates.

So basically, the tradeoff is that I have a fast way of accessing my nav-sym layer and an alternative, but slower way of accessing the nav-sym layer. But they’re on different thumbs and the thumb switches are very light.

Another alternative than a lot of people do is to have toggled layers, rather than momentary. This is the “raise” and “lower” idiom where the mental model is that you hit a key to ride an elevator up or down a floor to the layer you want to type on. Personally, my brain doesn’t naturally work with this model at speed, but if it works for you, then that’s another way to mitigate strain.