In an ideal world I think enough in savings to cover all household costs for 6mo should be the minimum you aim for, to cover job loss, sickness etc
just having enough to cover mort for three months isnt enough it has to cover petrol, food, other bills
and I would say min 6 months.
we have only just started to save, dh has small salary increase, and its spread everywhere!
50 onto savings a few thousand, 50 onto a kitty for the dd's which covers clothes, shoes, school trips. 20 towards xmas, 10 towards bdays, 20 towards next years holidays, and so on and I also add to this. so we have lots of savings all slowly building up. to feel comfortable though a base of 20 grand would make me feel more secure.
talking of other income if you have an extra bedroom you can always rent it out in dire need...
your still v young op, if you can start to save more it will be brilliant for you.