I went through all all posts manually and marked them with "only me" as custom privacy and "hide from timeline". What I now need is a tool that I can run on a monthly basis to automatically do this for any content older than a month.

I don't mind making inane posts on Facebook which friends can comment on as that post shows up in their newsfeed, but once enough time has passed for it to fall off the newsfeed then as far as I'm concerned it can be permanently deleted.

P.S. I've started referring to logical deletes as "Facebook deletes" in work.