Can I file with the free edition if I've been using the paid edition for years? I have simple returns for both federal and state.

Yes you can use different versions each year.  There are 2 free versions. In the regular Turbo Tax Free Edition, information that you can enter is limited now.  Why do I have to upgrade from the Free Edition?
https://ttlc.intuit.com/community/upgrading/help/why-do-i-have-to-upgrade-from-free-edition/00/26379

To go back to a lower version or the Free Edition you can try to clear and start over https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-clear-and-start-over-in-turbotax-online/00/26444

OR There is also The Turbo Tax Free File program which is free for federal and state.  And has more forms than the Federal Free Edition, like Schedules A, B, C , D, E, F, EIC, H, K-1, SE,  etc.

To qualify for the Free File website  you just need to meet one of these 3 things
AGI $39,000 or less
Active duty military with AGI of $72,000 or less
OR qualify for EIC (earned income credit.)

In order to use the Free File program, you have to start it at a special website. Try signing in at the top right
https://freefile.intuit.com/