Alessio,
This is a bit difficult as most E type owners in the UK and US are gentlemen of, ahem, a certain age who have acquired tools over the years or inherited them from their fathers and uncles. I have shed full of tools which I did not buy! And since the seventies, we have been increasingly infected by metric so imperial-only is getting hard to find except second hand on eBay.
When I have come up short on a particular fitting I use this chap who does mail order -
http://www.baconsdozen.co.uk. IMO he is very good value and completely reliable.
However, I am unable to walk past a hardware store without buying something. I also have two homes in different countries, so I tend to double up on kits, or at least justify their purchase to my wife on those grounds...
Will you be buying in the UK or buying remotely? Some offers require you to be in store.
I have in whatever car I'm driving, and like, the Laser 3571 42pc Alldrive (IIRC around £120) - this is a good all round kit with spline, star, AF, metric and Whitworth attachments, and the ability to procure extra pieces in those standards. The set includes 17 half-inch drive sockets and 19 30mm-long bits, plus a 72-tooth oval ratchet, extension bars and universal joint. There is also more basic kit at around £45.
Alternatively, for the shed, especially when it has one of its many promotions, the Halfords Advanced Professional 150 piece set is very good value (around £100 in most sales but I bought mine for £35) - (
www.halfords.com). There are bigger multi-drawer sets, often on offer, too, if you happen to be in the UK at the right time with a car to drive the cabinet back in, or if you can persuade someone to obtain one for you for when you can do so. Please note that many people (including professional mechanics) in the UK swear by the Advanced Professional range but do not rate the normal Halfords stuff so well.
Where in Italy are you? I understand that it is not practical not to have your own set of tools at hand but I might be able to help out/lend tools in an emergency. I live near Stresa (VB) for about half of the year.
Peter