Yes, you are going down a rabbit hole. Never put 2 layers of felt here. Reducing the dip that much will make the action feel choked/heavy, then raising the rail creates more issues that need to be dealt with.(key height, hammer stroke, escapement,damper issues)
Just use ONE layer of back rail cloth. The secret to reducing the noise is to NOT PUT GLUE directly under the part where the keysticks actually touch the felt. Only put glue (lengthwise,across the keyboard) on 1/2 of the felt where there is a gap between the felt and the keysticks. As wood glue hardens, it may cause a clicking noise when the keys fall back to their rest position.
It's not so much the thickness that reduces noise, but the softness of the felt.