I would suggest you talk to your OBGYN about your concerns and get some ideas.
I do know that you can get pregnant while still breast feeding however it does effect your hormones.
I would say you need to give your son the gift of falling asleep himself and not use breast feeding as his pacifier or soother.
It seems from my friends it is the moms that have the tougher time weaning, he is almost 2 and doesn't need to be breast fed and if he does it to fall asleep he isn't learning to fall asleep himself. You can reduce feedings and finding other means to soothe him at bedtimes, music box, new stuffed friend but I personally would do it all at once and get it over with while getting him out of your bed. Make it a big deal to be a big boy, hold him, rock him but lay him down awake!!! Get him a big boy bed, let him pick out the sheets and so forth, give him a chart for every night he does well with a reward of what he likes.
It is never easy to transition a child, however you have to be willing to go through some tough nights, tears and all that comes with it. He won't be traumatized. Pump and offer only sippy cups of breast milk, or strawed cups.
He needs you to be okay with the changes and standing firm and it will be easier when your breasts dry up. He needs milk for the Calcium and Vitamin D. I think we hang on as we don't want to lose that baby connection but now you have a toddler that needs to gain some independence and learn to self soothe, sleep on his own, it is a gift you would be giving him.
Good luck, stand tough and realize it is a good thing you would be doing. Doing all this before a new baby comes into the family will help him adjust a lot better to that change too.