My DS (12 weeks) seems to really want to suckle as a self-soothing trigger to sleep (and may also be related to mild reflux we are currently treating). It almost doesn't seem to make a difference whether its his thumb or my pinkie finger or my breast. I have actually tried to replace all the above by introducing a dummy at our (infrequent!!) nap times and bed time, but he hasn't taken to it at all and spits it out, crying for either his thumb or my finger/breast.
I have been giving this some thought, having read some of the soother vs dummy threads and am really confused and would love to hear some MNers experience, advice and/or suggestions.... 
I am wary of letting him suck his thumb, because I aware that it's a really difficult habit to break, so much so, that there are many adults in their 30s/40s still privately sucking their thumbs. I'd prefer my DS not to have this potentially lifelong habit. On the upside, I know that his thumb will always be there and he can self-soothe whenever he needs/wants.
I could try the dummy again at naps and bedtime to help him settle and remove it at about a 1 or 2 years when he can understand that the dummy fairy has taken it and have one hellish week to deal with. This way, he wouldn't have a lifelong habit, but I do run the risk of him crying and waking for it throughout the night desperately needing the dummy to self settle...
Thing is, won't any baby/toddler just automatically substitute a thumb for the dummy that gets taken away after some time using it? I mean, babies/toddlers seem pretty resourceful to me, and it seems a fairly logical substitution to make...
Sooooo.... does this all mean it's better to avoid both the dummy and the thumb??
If so, how do I help him settle when he soooo clearly wants (needs?) to suck on something?
Am I overthinking all this, and should just let him use his thumb and/or dummy? 
Arrgh! Your experience, thoughts, suggestions needed - and apologies for the long, rambling, sleep deprived post......
x