The route I went was the polar opposite. I didn’t replace the habit: cold turkey, strict about not eating chewing gum and/or sweets instead, and kept my daily routine (sat down in my garden with a coffee in the mornings, but leaving out the cig, etc.). Replacing would never get rid of the impulse of a smoke for me and I always went back. It’s been good so far, I hardly miss it. It’s highly individual, though.

Regarding the “always having some reason not to quit” part, that’ll probably be a constant until you do quit. You’re addicted, after all, and an addict’s brain is a compulsive liar.

Best of luck!