what is the best image for db: and db_backup for sqlite on docker-compose?
To answer your question sqlite dbs are file based DBs and they are updated using libraries. So the only thing that matters for them is the file location, you don't access them over network. So you don't need any additional image or service for hosting sqlite db
The only thing you need to make sure that your image/service where you need to access the sqlite DB has the required libraries. You can then use volumes to save the DB on host if needed. So your sadmad/ibuy7:1.0 image should have the required libraries.
Also if you want to use network based DB then you should use the official mysql or postgres images
I can suggest you to use the image of https://github.com/jayniz/docker-postgres-s3-backup-via-cron to do cron backups to S3