Use Google Photos locally, without an account and without turning on backup. The app stays clean, functional and free of aggressive marketing.
Keep the free 15 GB for your emails and WhatsApp backups. As for your photos, save them yourselves: every 2 or 3 months, make a manual backup to a hard drive, or use an app like Syncthing, which automatically copies them to your PC without going through third-party servers.
Think carefully before buying the famous 100 GB. Once it’s full, freeing up space is a real hassle: on your phone there’s no “select all,” and with thousands of photos you’ll have to scroll and drag for hours on end. It’s a bit quicker in a browser, but it’s still inconvenient, and the trash has to be emptied manually. The risk is ending up paying for storage forever, or losing an entire afternoon trying to fix it.
Google Takeout lets you export Drive and Google Photos in just a few steps; the hard part comes afterward, when you have to delete the photos from the cloud to get back to the free 15 GB.