What kind of gloves could I wear before manipulating electric wires if I really want to be safe even after having turned off house electricity? And where to buy them?
If the electricity has been turned off, and you have confirmed it's off via a non-contact tester, multi-meter, or some other method, then you don't need gloves to protect yourself from electrocution - there should be no risk if you've actually confirmed it's off. I even go as far as to put a piece of tape over the breaker so someone doesn't walk by and flip it back on.
I sometimes wear gloves to protect my hands from scrapes and cuts - any work glove you find comfortable for the job should work.
As DA01 said in a comment, a glove that would protect you from shock would likely make working with the wire/cable we find in residential difficult. They do however make insulated tools which can be used when working on live gear. Best to just turn the power off and not worry.
The best thing to do is not work on or around any thing energized. DO NOT work on anything energized with gloves that are not designed for that purpose.
If you want to learn about electrical protection then go to this website.
For the short answer you need two or three gloves to handle energized circuits. All have to be rated for the voltage you are working on. The first pair is optional, they are for comfort and warmth. The second pair is the rubber gloves. This is where you get your protection. They come in different lengths and even sleeves. The third pair is leather to protect the insulated gloves.
You can't just buy these anywhere, and since you did not know about these I beg you not to attempt to use them. Very few licensed electricians have or use these.
Gloves can be bought at many DIY stores - they are labeled as gloves for electric works and rated for some specific voltage. However gloves alone don't guarantee protection. It is possible that some energized wire touches your body above the glove and you can get shocked. This is why a lot of other insulated protective gear is used by the electricians - insulating mats, insulated ladders, etc - and working on or near energized wires is strictly regulated (by something like USA National Electrical Code or an equivalent in other countries).
One major factor is that wires are rather hard and so their edges are rather sharp and so they can easily cut through almost any glove or damage the glove and weaken the insulation. This is why you use pliers with specially insulated handles to work with energized wire edges.
That said, if you are sure (you have tested and you're really sure) that the wires are disconnected and not energized you can just work on them without special gear - however some basic tools and gloves to protect you from cuts would not hurt. If you are unsure about whether the wires are energized then you'd better work according to the regulations and in that case I'm almost sure gloves alone are not enough.