I'd do a biscuit to butter ratio of 2:1. So 1/2 the weight of butter to biscuit. Re biscuit, you want one that's not too dry. Flakey/crumbly base sounds to me like it's too dry. So no to rich tea, oreos or 'nice', unless you want to use more butter. Shortbread probably a bit too buttery. Digestives are good, whether chocolatey or not.
The you want pat it down evenly, but don't push it down. If you really compact it, and then chill it, it'll be impossible to cut.