Thats my take on a very simple spoolholder. You can simply fit it onto the 3/4"x1.5" wood. The second design is very similar but using a T-beam instead of full material thus redusing filament usage but probably adding support structures.
The dimensions I used for a dummy spool are the extremest I could find online so most spools (probably except for for example 5kg spools) should fit.
If my design should break somewhere it would probably be at the right angles of the wood so adding a curve there and sanding the edge of the wood down will definately add stability. Thats what the second pair is made for.
As my printer is yet to be delivered I unfortunately wasn't able to print and test it myself.