Any amount of soy can cause hormone changes and each person reacts differently, but especially with boys, I would keep them away from as much soy as possible, since it's in nearly EVERYTHING.
My boys weaned themselves to 1-2 nursing each day by around 16 months. At 12 months, it looked that there was no end in site, but they both transitioned quickly - child led.
Goat's milk might be a better choice, or better yet, pumping.
These stats are from thw World Health Organization:
Babies who are breast-fed for at least 6 months have fewer health problems than formula-fed babies, including:
3 times fewer ear infections
5 times fewer urinary tract infections
5 times fewer serious illnesses
7 times fewer allergies
Breast milk is so easy to digest, breast-fed babies spit up less often, have less diarrhea and less constipation. Breast milk actually starts to digest in 90 seconds.
For every 87 formula-fed babies who die from SIDS, only 3 breast-fed babies die from SIDS.
Babies who are fed ONLY breast milk (no supplementing with formula or solid foods) for at least 26 weeks (or 6.5 months) are 6 times less likely to develop lymphoma (type of cancer) in childhood.
Babies who are breast-fed for at least one year are 50% less likely to develop diabetes.
Breast milk can begin a lifetime of good health for your baby
As adults, people who were breast-fed as infants have:
Less asthma, allergies, and diabetes
Fewer skin problems, including dermatitis and eczema
Lowered risk of heart attack and stroke due to lower cholesterol levels
Less ulcerative colitis
Less Crohn’s disease
Protection from certain chronic liver diseases
Breast milk is brain food. Studies show that children who were breast-fed have higher IQs that those who were given formula.
Breastfeeding is healthy for mom
Women who breastfeed lower their risk of cancer.
Nursing for a lifetime total of 2 years lowers the risk before menopause by 40%
Nursing for a lifetime total of 6 years lowers the risk before menopause by 66%
Nursing for a lifetime total of 7 years lowers the risk of breast cancer throughout a woman’s life to almost 0%
Breastfeeding your baby also provides protection from cancer of the ovaries and osteoporosis.