I have been sucking my thumb for 63 years (I'm 63) except for the time I was in the US Army (3 years).
I do have some pacifiers and I use them occasionally but I always go back to my thumb. It is always available and I find my thumb to be more comfortable than my pacifiers.
Not going to lie this is a habit I've tried to pick up before but it's not really all that much for me.
It's nice enough, but my paci is nicer. I'm also really conscious about microbes and dirt so I can't suck my thumb unless my hands and nails are 100% clean and washed and haven't touched anything else at all.
I've been sucking my thumb more and more recently. Sucking my thumb really helps me regress into little space more than my pacifier. I still like my paci but my thumb is very comforting.
I like to start with my thumb but eventually end up trying to get my whole hand in my mouth. I get very drooly with my shirt ending up pretty wet. But it's definitely my paci in bed for sleeps.
Like Geo, I find it comforting to have something in my mouth while I'm being dressed or changed.
Whether the 'something' is a pacifier, bottle nipple or my thumb isn't particularly important to me.
I'll suck my thumb if I'm not offered a pacifier, but the paci is still my first choice. However, my nanny says she enjoys watching me suck my thumb. She says the paci isn't as 'cute' as thumb sucking.