it's worth trying with the manufacturer but I wouldn't get another pram. Another 6 months, your DS might not be so keen on riding in the pram. And if your baby wants to be worn (mine did especially when they were little), you have another 6 months where ds can go in the pram while you wear baby.

My dd is 3 and although I have a toddler seat on the pram, it is rare that both kids are in the pram. One is being worn and the other in the pram or DD is walking and ds is in pram or carrier or walking.