Hi Sir,
I am Nathan CEO of an Odoo services company based out of Techno-park Trivandrum.
We have already done multiple Odoo version upgrade projects.
From 8 to 9 and 8 to 10.
Please review our odoo profile feedbacks.
We are our own process to do the upgrades and our developers are aware of the issues that might arise during the migration.
Since we have already did similar projects, we repeat the same success for you too.
Thanks and Regards
Nathan G