I started with PrestaShop, then switched to a different package and later switched back to PrestaShop 1.7. I'm now running PS 1.7.8.11. I tried updating to 8.2.1, but it failed. Updating to 9.0.0 wasn't possible directly.
I then created a subdomain to install PS 9.0.0. I then analyzed both databases to transfer the data myself. I've now written SQL code to transfer my data.
I chose to use the Hummigbird template. I think it looks very nice. And now that I've transferred my images and adjusted the colors, I think my website looks much better.
But as others have mentioned, there are still some teething problems. It's a shame I couldn't upgrade from 1.7 to 9 all at once.