A safe height is one you have thoroughly planned not some arbitrary number: including surface obstructions such as tall masts and of course high ground, glider and parachute sites, not forgetting notified airspace, "if I need to then I'll divert when I get there". There is little to be gained by having a minimum of 3000ft agl in the UK when you cannot fly that owing to notified airspace or cloud bases which are typically between 2-3000ft and lower.
I find it depressing how poorly navigation is taught: no low level operations training, unplanned diversions skipped. Flight solely by instruments totted up to meet the 2 hours demand but the content almost non-existent, "all that is required is a level 360° turn", no it isn't, the syllabus is detailed and comprehensive but this is ignored.
I used to know a guy who insisted that on light GA aircraft his personal IFR minimums were VFR.
This is clear of cloud with a visibility of 1500 metres and a minimum height not specified by ICAO.