I think Apologia has a middle school "general science" that covers all of those fields?
On that note, in most public schools science is still integrated in middle school, so a general science may be a good idea. If you are going for "depth" over "breadth", you could do a rotation of life science, earth science, and physical science (one field per year).
i used the apologia books with all the kids no matter what age, 5-15, those are greaat books! right now the 15s are using the general science book,
heres an idea from one scope and sequence what 7th graders might learn
* Scientific classification * The cell * Heredity and genetics * Effects of weather and climate * Properties and uses of water * Atmosphere * Air pressure * Rocks, soil, and minerals * Ecology and environment * Conservation * Heat and temperature * Laws of motion * Energy * Scientific method * Laboratory techniques and safety