It's great you want to make the change to GOS, welcome to the community! If you really require a service, let us know your country so we can give you better advice since many services don't send the phones everywhere.
Like most people I'd recommend you do it for yourself. It's easy with the web installer and people here are available to help you if you have questions or need assistance during install. Just make sure you buy an OEM unlocked device (directly from Google or a trusted reseller) and follow the steps exactly.
And if you don't have a device yourself for installation, maybe a friend can borrow theirs (e.g. any somewhat modern Android smartphone will probably do the job).