We have this problem very often. Due to my son's developmental delay he frequently grows out of things he still needs because he gets too big for them.
For example, he still sleeps in a sleeping bag. He loves to cuddle underneath a blanket - for approximately two seconds. Then he shoves it into one corner of his bed. We have tried to wean him from the sleeping bag and get him used to a blanket but it does not work. All we achieved was having a freezing child being curled up to a ball in the other corner of his bed. Because I was quite sure what would happen I checked on him approximately 10 minutes after I turned off the lights so he did not freeze a whole night. But still. He is too big for sleeping bags that are sold regularly so the next sleeping bag I will have to buy will cost us a fortune because it will be a custom-made product which triples the price. Same goes with his pyjamas that are onesies, too.
Or take his special needs buggy. When he got too big for the buggies that are usually sold he was far from walking good enough to get rid of a buggy completely. So we had to apply for a special needs buggy which costs around 2500 Euro. Luckily and after much back and forth discussion, our insurance company granted it.
When he grew out of his crib we had to apply for a safety bed because only in another universe could we have changed him to a big boy bed and there were no larger cribs available.
It happened with so many things already. He does not really fit into a high chair anymore but when we go out for something to eat the only way to keep him from running around constantly is putting him in a high chair. The last time we were out we hardly could not get him out of the chair anymore because his legs are too long by now. We will definitely not be able to use the high chairs that are offered at restaurants any more because they only have the ones for babies/toddlers. Which leads to the point where I have to become innovative and think of a solution. I might even have to craft something - and this is where the problem starts because I am not skilled at crafting. At all. But very often I have no other choice but to come up with something handcrafted because there is just nothing available on the market to help us with what we still need.
Another thing I am occupied with at the moment is finding a fitting potty. I do not normally talk about potty training here because I think this is something too personal that is only Sunny's deal but in this case it is more about the potty itself. I found out that Sunny is uncomfortable with using our potty seat for the toilet - for whatever reason he does not want to stay on the seat for more than a second. I have a feeling that he might be afraid but I am not sure. Anyway, I thought about getting a potty because I figured he might prefer that. But boy, almost all potties are way too small for him! I searched online for hours on end and finally decided to order about 7-8 different ones and just see how they fit. I think I finally found a solution. There is one potty that is really cool; the housing is bigger and higher than the others so he is able to sit comfortably. The problem with this one is that the part you can take out to clean is too small. It is actually tiny. But I found out that this respective part of another potty that I also ordered and which is quite fitting, size-wise, miraculously fits the housing which is comfortable. So I guess I will just have to buy both of them and combine the parts.
It just never gets boring and keeps my creativity going! :-)