Looking to put in raised beds (of varying height 200mm to 450mm to break
them up a bit) it's taken me more than a decade to come up with this
cunning plan, so I'm hoping not to hear a chorus of "terrible idea",
"don't do it" or "you'll regret it" ...

Looking at using new untreated oak sleepers direct onto topsoil, or
should I consider treated softwood instead?

I'll have a fair quantity of topsoil to fill them with from levelling
other areas, just lob that straight into the beds or is it worth some
coarse aggregate in the bottom, especially of the deeper ones, for drainage?

Thanks ...