I am currently trying to figure out how to go from an on-premise (one customer/one server) installation type to a SaaS web app distribution. To give you more context about the application, it manages companies internal quality controls (product and raw material controls). The idea to go to a SaaS distribution emerged because some of our customers do not have an IT infrastructure and it's tricky for them to maintain servers on their production site.
To clarify my question: Our software currently does not manage any kind of data isolation. Would you recommend to implement data isolation on the software side (by somehow "tagging" data with its owner and filter request based on that) or redirect user according to its company to a different data context (different database/schema) and make no change about software interaction with data ?
As for frameworks, we currently use Python3.7/Flask/SQLAlchemy, but I'm really asking for best practices here, not really code-wise implementations.