Have you looked into MakeHuman? It's a free and open sourced character creator that has dynamically scaling body rigs, even the face's blendshapes change according to the changes made to the model. The models it makes can be imported into Unreal and Unity I believe as I've seen guides, but I've only really just started messing with the software so I'm not 100% certain.
The main downer about MakeHuman seems to be its general lack of clothing and hair options. There just isn't enough user-generated content for this software to really make up for the lack of built-in content.
But hey, it might be worth trying since it's free and all.