I know you have already made up your mind to wean him. I just wanted to let you know that breastmilk is by far the easiest thing for babies/toddler to digest and there is no other food that will substitute for it. I did not nurse either of my babies but I pumped for them for a time. When I was ready to quit pumping for dd2, in part because she was not tolerating something in my milk and I was tired of trying to figure out what, I expected that I could just put her on soy formula and all would be fine. It wasn't. She ended up on a hypoallergenic formula that cost an arm and a leg. She ended up having digestive problems in general and I find myself with her at 30 mos old still buying formula sometimes when she's having bad days. If I could have looked to the future I would have kept pumping and elimited more things from my diet. She gets very sick over the winters and breastmilk would have helped her.
Before you wean, make absolutely sure that he can tolerate something that has the same protein and calcium and other nutritents that breastmilk offers. Rice milk is *not* a good substitute for growing toddlers. It has almost no nutrition. No fat, low protein, low vitamins. Same with soy milk, although some vegan parents will add things to make it work. It's still not as good as breastmilk.
My daughter, who has severe feeding issues, survives a lot of times on Pediasure which is lactose-free, or by ordering a special soy pediatric formula on-line for $$ when she gets really bad. Pediatric drinks are "dead" food and hard on the kidneys to digest. They are canned and manufactured and not even close to natural milk products. Certainly not something I would have chosen in my own. Breastmilk and other natural milks are alive. There are pediatric drinks that are for kids who are allergic to dairy and soy but they taste awful and are extremely expensive, like $8 per 8 oz can. Most kids who need those for survival (severe allergies, not growing or thriving) end up with feeding tubes because they won't drink it by mouth.
I am a member of a forum of kids with feeding issues. I have seen and heard of kids who weaned and within months became failure to thrive and got malnourished. Kids for whatever reason could not tolerate milk or would not drink milk, and would not eat other nutritious living foods that had the same nutrients. Some ended up on feeding tubes, some just remained malnourished and developed a lot of other related problems such as constipation and behavior problems. I have seen it happen over and over again. I don't want to scare you but I want you to know what can happen.
Weaning is a personal decision and if you need to wean, I can respect that. But your child needs to be eating or drinking something that has the same nutrition he's getting now in bresatmilk in order to grow and thrive, or you may end up with a malnourished child. Nutrition is the most important thing in the early years and being malnourished will affect a child for life.