I'm recording some voiceovers at work with a voiceover artist I work with (we're a talented bunch at our place

), but I'm finding it difficult to monitor ambient noise properly as my headphones don't isolate enough.
I'm doing all I can to isolate her voice (reflection filter, close mic position, a good shotgun mic with the vents appropriately positioned to reject the noise source, good levels etc) but I'm a perfectionist.
I don't get on with in-ear phones because I have very small ears and my right ear canal is slighty mishapen.
So I want some phones that cover my ears and provide the kind of isolation that you'd get from a set of builders ear defenders.
Any suggestions? I'm prepared to spend quite a few bob as I see it as an investment for future work.