Hi ExpatPumpkin and welcome to FT.

If you're making £50K per year, the very useful listen to the taxman website indicates you'll have a hair under £3,000 per month in disposable income.

Spending £350pw on rent is £1,516 per month - which is more than half of your UK income just on rent. You also have to count utilities (add another £70-80) and council tax (add another £100), as well as Tube fares (monthly travelcards for two people, add another £200) and food (just grocery shopping will set you back between £150-250 depending on your tastes). This doesn't count going out for dinner, drinks, the odd show, the odd cab, and of course shopping for yourselves in case you need new clothes or electronics.

You mentioned that you will live on the Piccadilly Line - is this absolutely essential? If you don't mind my asking, in which area of London will you/he be working?

If the Piccadilly Line is essential, you may wish to consider Earl's Court or even slightly further out, like Acton Town. These places will be closer to LHR for you, but are only 10 minutes or so further out from Hammersmith/South Ken. The value-for-money of housing is far better in that area. Don't go as far out as Osterley or Hounslow. There are pockets that are not so nice and it's right under the LHR flightpath.

If I were you, I wouldn't use my savings to supplement my lifestyle, especially not when it's going towards rent which is not getting you anything tangible - you'd just be just making someone else richer.