I totally get the hesitation with the cost and hassle—my place is a 1950s ranch, and I dragged my feet for years.
Had a similar situation in my ‘60s split-level. Heavy curtains helped, but like you said, “Heavy curtains are a band-aid; new windows actually address the root issue.” Ended up going with triple-pane in the main bedroom—thermal performance is noticeably better, especially on windy nights. Still, the upfront cost was rough. If you’re not planning to stay for years, I’d lean toward just sealing gaps and using thermal curtains. The ROI on new windows takes a while unless your old ones are really shot.
Triple-pane’s definitely a big leap—seen plenty of folks shocked by the sticker price. But you’re right, curtains only do so much. I’ve replaced windows in houses where the drafts were so bad you could feel it standing a few feet away. Still, if the old frames aren’t rotting or warped, sealing and thick curtains can buy you time. Not glamorous, but it works for a while.