Yes maybe one sleep a day could be worth a try. Maybe from 11am? Then bed at 6.30pm. I did that with both of mine, and it worked well. I also persevered with the sleeping because they had to know the bed was for sleep. I would go and pat, but never got them up once they were in bed.
good luck xoxo
PS DD2 had allergies too and we used Goat's milk, you can get that at woollies/coles. It seemed to go down easier than soy.