Sure, please do that. I would be happy to help you in optimizing your queries, if possible. Also, please share the schema for your existing service, which will help me understand the data better.
And, re-reading your post again, I got some more insights.
The data-type for the Data.value will be different for different kinds of data. In GraphQL, the type system is very strict, unlike a document-based model where you can just dump any kind of data.
What I feel here is that you should have an interface Data which represents data as an abstract entity. And, then you can have different implementations for it, like SleepData for which the value will be an Int, GpsData for which the value will be an object type consisting of latitude and longitude, etc. That way you will be able to answer questions like this straight from the db: