>>328048019
If it's a static prop, attaching it how you've been doing it in unity is fine and probably the most performant. 

If the prop is almost always toggled on (but still want to occasionally toggle it off), like a hat or something, you can use blender to attach it to the main armature. CATS blender plugin has a nice button to do it and assign the proper weights, but it's simple to do yourself too. Then once you have the prop attached, you can add a shapekey, in edit mode select your entire prop, and scale to 0, then use the shapekey in unity to implement your toggle off. Alternatively you can weight the whole prop to a new bone and shrink the bone in unity to 0.