Old ID for Itunes but new Apple ID

I set up an Itunes account in the 1990s, before Icloud etc. Then when Icloud came along [or a new computer, cant recall] I set up a dfiferent ID. Dumb, I know. For yeaars Itunes worked with the old account, automatically. But now it doesnt work. APPLE DOES NOT ALLOW ME TO SWITCH MY ITUNES ACCOUNT TO MY ICLOUD ID. Someone on this site said I would neeed to set up Family Sharing [for which I have to pay money] to accomplish this but warned it could be "kludgy," whatever the heck that means. I can only figure out that ethical, beloved Apple is herding people into the new Apple competitor with Spotify. But i like Spotify, do not want family sharing. I just want to change the ID on my Itunes account. I might be simple if I knew the password from the old Itunes account but Im 70 years old and who cn remember an ID from thirty years ago. WHAT CAN I DO -- WITHIOUT GIVING APPLE MORE MONEY? Grrr. I wish I werent trapped in the Apple moneysphere