OK - first of all, let's get one thing clear.
I assume that you would be using screwdrivers to remove and replace the switch and socket, connect the wires up etc?
i.e. I assume that you have screwdrivers in your tool box because you recognise that they are the right things to have, that using the point of a knife is not right, and that if someone
decides that they
want to do things with screws then they should get screwdrivers?
Multimeters have exactly the same status when it comes to electrical work. As you have
decided that you
want to do electrical work then a multimeter becomes as essential as screwdrivers.
I don't really want to have to buy a multimeter, as it's a one off thing
But it's not.
This is the 2nd electrical job you've posted about, and I doubt it will be the last, given that you're doing significant refurbishments to a house you've recently moved into and are contemplating major building work.
Buy a meter.
This looks ideal for a household starter set - multimeter, voltage indicator and dedicated continuity tester, all in a handy case:
http://www.amprobe.eu/de_DE/showproduct/115/Junior-Set/
PDF brochure:
http://www.amprobe.eu/de_DE/downloadfile/115/beschreibung_1/
All in German, unfortunately, as is the blurb on each product:
Multimeter:
http://www.amprobe.eu/de_DE/showproductdata/487/Hexagon_55/
Voltage indicator:
http://www.amprobe.eu/de_DE/showproduct/116/2000_α_(alpha)/
Continuity tester:
http://www.amprobe.eu/de_DE/showproduct/481/TESTFIX/
but it is sold in the UK - the company is now owned by Fluke, and I guess they haven't got all the websites sorted out yet - contact them (
http://www.fluke.co.uk) for info on where to buy.
Right now the English specs are still lurking on the Internet Time Machine from when Beha was an independent company:
http://web.archive.org/web/20060920022629/http://www.beha.com/files_uk/multimeter/93549.pdf
Also see another discussion here:
//www.diynot.com/forums/viewtopic.php?t=26282 It's a few years old, so specific model number advice may be obsolete (and prices will be higher), but the generic advice is still sound.
If you don't want to buy a meter then don't do electrical work.