Hi MAsleeper,
I’m not danl of course but there is some generic information about split layering in post #2 here. It very unlikely that you would feel the split itself with any latex mattress with a quilted cover similar to the cover used in the Spindle mattress although of course you will be able to feel the transition in firmness between the sides.
Hopefully danl will add his comments that are more specific to the Spindle mattress.
Phoenix