Hey! You do _not_ need to purchase again. MiniMeters v1.0 is a free update and will continue to get free updates probably until v2.0 (which is not even something I'm considering at the time of writing).
If MiniMeters isn't in your purchases list in itch.io, try getting new download links by going here: https://itch.io/docs/buying/already-bought
If that doesn't work, send me an email at contact@minimeters.app and I can do some more sleuthing to find your purchase.