I would suggest a modified version of the FOIA-mechanism, which is where the FOIA (or perhaps other law but keeping all together is fairly important) specifically incorporates certain already societially-recognised importent sets of information for automatic release.

This has come about in a number of countries (not the UK alas) because of public pressure which is then recognised and incorporated into law by the Parliament. Its limited in that there are always going to be lots of sets and you dont want to clutter up things more than they already are (cf FOIA 2000) but at least some bare minimum things are public like contracts, budgets, etc. without having to go through the sometimes labourous process of FOIA or hoping they will get released under OD. But then you always have the law as a backup to get it if there is a selective release or some body doesn’t like the way you used it and decide not to make it public again or only release selected bits.

Dave