I use a 4 inch glass bowl (very heavy bottom) and currently aspen (sani chips) although I am switching back as soon as it is gone to coco coir. It is cheaper and has less issues with getting stuck under scales (why I tried aspen in the first place one snake of 11 got some trapped under a scale in 3 years I have had 6 times in 8 months with the aspen)
I actually humidify the whole room in the winter as it naturally is in the 18-22% (@ 80ºF) range. In the summer I don't do anything as it runs in the 60% area (@ 80ºF)
If your ambient air temps are 75-77ºF area you likely want to target 70% during sheds as that is 15.5gm/m3 of water. RH is relative to temperature. 15.5gm/m3 is actual humidity it is a constant.