Hello, ZipZap1978. Thank you for posting to the Apple Support Communities. We understand your situation and how you are looking to keep your messages and data in sync across both of your devices. We’re happy to explain the available options that you should have for this.
From what we gather, you currently have two devices that each use a different Apple ID. As it turns out, we typically suggest that you use the same Apple ID account with all your devices. This will allow you to keep your messages and other data in sync with your devices. If you currently have two Apple ID accounts, we would suggest that you start to only use the one account with the most data saved to it at this time.
Once you have decided which Apple ID account to use going forward, you can enable Message in iCloud to keep your message history automatically updated on your devices. The following Apple Support article explains how you can enable this feature for your devices:
Use Messages in iCloud - Apple Support
In addition to this, you can use this next article when managing iCloud features on your devices:
Turn iCloud features on or off - Apple Support
We hope that this answer provides you with the information that you need to set up your devices and keep your data in sync. Please let us know if we can help answer any other questions.
Cheers!