There are so many different ways to explore your options without jumping into another degree, but everyone has different preferences. If you're stuck on going back to uni;
You should check around, see if there are any MSc options in the Biomedical Engineering field that you can join with the modules you've done. Mechanical Engineering can open doors to so many different fields including the medical areas.
You could also try to find an apprenticeship instead of another traditional degree so that you can have some money and hands-on experience while studying.
If you're willing to try something else other than uni, just work. Work and float between different fields. You'll definitely find a lot of options to explore in the industry.