My friends, put a Band-Aid on their nipples and they said it totally worked for them. Their children were also 2+ years old. They would tell their kids that "Mommy's milk is broken" or they have a owie.
Other friends have told their child they can only nurse at night-time....
Since your son is using you as a pacifier and it is quite obvious... and for anytime he is upset or transitioning to something else... you would NEED to teach him some "coping skills." A child this age, does not have coping skills, yet.
For me, my daughter self-weaned at about 2.5 years old. BUT she did not use me as a pacifier... I still had milk and she did 'drink.'
But for her, I would stand-up and make myself "busy" if she wanted to nurse more often... and I would say nicely "Mommy is busy.... hold on..." then I would busy myself with other things. And within a minute or 2, she would be distracted with other things.
ALSO, if your son is throwing fits when you deny him (my daughter didn't do that)... then perhaps its about time you talk with him about it, in an age appropriate way. (I did that with my daughter too) telling him "One day, you will need to stop...." you are a big-boy.
Try giving your son a "lovey" perhaps, or a doll that he can take care of... something else that HE can "comfort." This works for some kids.
The hope is, that he will self-wean... as you said you don't want him to stop, but just do it less frequently. BUT... since he is showing MORE INTENSE interest in your boobs, for pacifying and comforting... you may need to have certain rules about it... ie: only nursing at night-time or something. A child that age will NOT understand that they "can" nurse but not that often. It is either all or nothing for a child this young. They don't understand "grey", only black & white, tangible things.
Your son is boss of your boobs.... if that is fine with you, then that is fine. But, let him know it is "your" body... and Mommy has to take care of herself too.
Or tell him "the Doctor said only nursing at night..." For some kids, doing this is something they can understand.
ALSO the fact that when he is at your breast and constantly "switching sides back and forth" and wants to be at your breasts EVERY 20-30 minutes, tells me that you may not have any milk. So he is going back and forth.... and is just using your boobs as yes, a pacifier.
I would start to explain to him... that it is not acceptable to do so... he will slowly catch on. For my daughter, I also emphasized "manners"... that she can't just lift up my shirt and grab me whenever SHE wants... that she must ask nicely and if I am busy, she must "wait." She understood. There were nursing "rules" which, when she got closer to 2-2.5 years old, I explained to her, age-appropriately and in a nice comforting manner... so that over time, she would "understand" that it could not go on forever, and that MOMMY was the "boss" of my own boobs.
I did NOT like to just have my shirt lifted up and my boobs grabbed willy-nilly and certainly NOT in public... she was older by then, and so I went according to her cognitive/emotional development. And she did self-wean when she was ready.
I am also assuming... that your son, by now, is drinking regular whole milk as well???? If not, then he probably should.
Just some ideas, all the best,
Susan