If you’re with SiteGround and already paid, there’s no reason to leave them. They are usually a decent hosting provider. You have to ask their support to disable automatic WordPress updates so they don’t update your ClassicPress to WordPress. We’ve discussed this in this thread.
DigitalOcean isn’t for beginners. That requires more technical knowledge. You’re looking for a hosting provider that uses a cPanel and offers either Installatron or Softaculous app installers. They make it easy to install ClassicPress without technical knowledge.
If you want to leave SiteGround, check out the hosting category for recommendations from other community members.
We host our own websites and clients’ websites, so I can’t personally recommend anyone specifically since I have no experience hosting ClassicPress with any other providers.
Hope that helps.