I have done it with bootlaces, and carry some in my bow drill demo kit. If you practice with good quality 4-5mm cord you hone your technique, which stands you in good stead for thinner more fragile cordage. Also when the 5mm cord eventually wears out, you are left with many thin strands which are useful for fishing line and many other jobs. A bow made from green wood is stronger than dead wood, again if you are a beginner your lack of experience may snap a weak bow. If you are using wood for your bearing block you ideally want green wood, otherwise you get hot ember dust on top of your hand!
Don't get me started on the woodlore bow drill method, it's not the best. I have given complete novices two bow drill sets, one woodlore and one greencraft. Every person who has done this with me says the greencraft way is much easier.
A bold statement, but true. There is more to bushcraft than the people lucky enough to be on the TV.
See you in the woods, let me know if you want a handout.
Luke