Adding faux baseboards /faux crown molding

I've seen a simple board added to the top of the existing board to update the mop board. I've also seen a strip of paint just above the board to widen the appearance. I haven't tried either of these. No input on crown molding...not a strong point for me.

If you want 3 dimensional - you will have to add something. Check other cuts of wood for something you like but cheaper than typical crown molding and baseboard. For instance, a 1x4 for baseboard and 1 x 2 for crown molding would work. If you have a router you can dress up the edge and more. You could plane &/or sand them without a router....work and time consuming but doable.

If that is not an option, you can tape off the distance you'd want and paint it on. At a glance it will give the illusion of something there but it will not be 3 dimensional. If you're adventurous and crafty, research trompe l'oeil which means to "fool the eye". That technique allows you to paint depth into it and it will look like the real thing.

I have also seen a half-round attached to the wall a couple of inches (or more) above the existing baseboard, then the whole thing painted to look like one wide baseboard. It works.

A good look for crown molding which is less than 4" is to paint a 4" +- band and at the bottom end of the band put a strip molding. Can do the same for baseboard, measuring up 2'+- and at the top of that put your strip molding. Hope that's helpful.