1. Move all personal pics and videos to cloud using Google Photos backup. Enabled auto backup.
2. Deleted all images and videos of WhatsApp which are just forwards. It will be a big chunk usually. Then backup them by including this device folder in Google Photos.
3. If you used to add contacts to Google account, it will be already backed up.
4. If any documents you have, say in Downloads/Bluetooth, which you need, then it can be backed up to Google Drive.
5. If WhatsApp conversation is important to you, then you can backup that as well in its settings to Google Drive.