Domain Name Selection Help

Hi all and thank you for months of educational and inspirational reading. Having learned a little the time has finally come for me to put the wheels in motion and take action.

Before I take the plunge however and register my keyword rich domain name I wanted a bit of advice.

Let's say for instance that my chosen niche is Envelopes and my target market is England (receiving 1500+ exact searches per month on G and traffic travis is advising relatively easy 4* grade) BUT there is also a reasonable amount of searches for envelopes london.

Bearing in mind that the following are already registered:
(As I'm new I can't post links etc)

envelopesengland
envelopes-england
envelopeslondon
envelopes-london

Would it be plausible for me to register:

envelopesengland-envelopesbirmingham

Or should I simply opt for something along the lines of:

we-sell-envelopes-england

I hope that I haven't made the above too complicated and I'd welcome your comments - Thanks in advance.