I get that not all debit cards are (pay ahead.) I thought that that was originally/maybe still an option, for reasons mentioned.
I've been fortunately a sufficient non-consumer that I do that (with a few early-on exceptions: when you had to Use the 'credit' to prove you Would pay-off.)

But as to 'teaching oneself 'thrift'--even with a running balance you can resolve that This-purchase I'll pay-off additional to whatever I pay on balance.
(And I realize that the intentionally corporate-favorable 'interest' calcs aka fees--probably make this a Pyrrhic maybe worthless victory.)

Do banks still do 'Chattel mortgages' ie "loans for non-real-estate Things"? I haven't looked at that in years.
Seems to me that, if you intend to run a balance for more than a couple months (there's already a big debt with CC-holder)
--couldn't most people negotiate lower rates than VISA et al? If it's practicable it wouldn't take a huge amount of planning ahead.