Comfortable -for me- in London is over 150k p.a at least
Btw, comfortable is a very individual state of mind. For me to be comfortable I'd need a house, you know a proper 3 or 4bed house with a very big back garden at a nice area, detached or at the very worst semi. None of that terraced 19th century crap.
Comfortable for me means a nice car, something that I enjoy driving and is luxurious to provide all sorts of comforts when I'm in it, not a bucket that takes me from A->B.
Comfortable is not needing to take public transport because a taxi is too expensive.
Comfortable for me is eating out at least twice a week, at a nice restaurant with a couple of good bottles of wine, not the local chippy with a diet coke or a pizzaexpress or other budget establishment.
Comfortable is to be able to afford 2-3 vacations a year wherever I like, including activities like skiing, scuba diving or whatnot. Experiences is all that we have after all and I want to enjoy the exotic things this world has to offer.
Comfortable for me is also buying the occasional gadget without having to wait for next months paycheck and planning it around my monthly bills. Yes, I'd like to be able to upgrade my computer, buy a tablet, a new smartphone or any other gadget on a whim because that's what I like and enjoy doing. Not upgrading my pc waiting for that second hand bargain or staying with a crappy phone because it does what I need.
Of course that's just me and that's how I'd like to live. That is comfortable for me, it's not well off or rich (that would be multiple properties, multiple cars, yauchts and not having to worry about working).
As for living within ones means, well of course you will live within your means whether you make 20k or 100k a year, what is that supposed to mean? You will always adapt to your earnings if you are sensible and you will always try to make the most out of life but that doesn't mean that you are getting what you wanted.
Of course all this will have to include the needs and wants of my wife and any children I may ever have.
As for the whole 'happy is having a roof over your head, pay your bills and food on your table' brigade, well excuse me for having aspirations and wanting to live the one life I got exactly the way I want it and not compromise. I live in one of the wealthiest countries in the world, in one of the biggest and most lucrative job markets with all sorts of opportunities and I don't intend to live my life like those who live at the poorest and have no better choice.
Of course each to his own and all that but this is what would make me materially happy.