Maybe runners’ earbuds? I’m not at all sure they’d be flat-spectrum and so on, but they are expressly designed to allow you to hear the bus before it runs you over…
I’m afraid the best I can do is point you here:
A second option is open-back headphones, that’s to say over-ear cans but with a mesh or otherwise “open” back instead of a solid wall between you and the wider world. Typically worn for mixing or mastering they’ll give you an enhanced stereo sound stage. You should be much better able to hear people creeping up, but you should know that open-back also means that what you hear spills out and you could be a bit of a human PA system. Certainly not the choice for listening to naughty audiobooks in a library 
(even writing that feels so awkward). A reasonably-priced pair: