Barley, buckwheat and spelt sourdough loaf

Hello, I generally make a spelt sourdough with sprouted rye grains (crushed but not milled). But for a change, I was thinking of making something along the lines of barley and buckwheat with spelt but not sure where to start with proportions etc.

Would you suggest using barley and buckwheat flour (the problem with that is sourcing fresh flour)? or soaking/sprouting the grains and crushing them?? I don't have a grain/flour mill, but I can use my coldpress juicer to crush them into a paste like I normally do with the rye grain.

Has anyone made/tried a loaf like this and how did it turn out?

Any other hints or tips welcome.

Thanks Heaps!