Hello Adrian - I'm in the US so I don't know what's available where you are - but after all my years of backyard feeding, this squirrel-proof feeder is the only truly squirrel proof one I've ever found, and it wasn't terribly expensive. It's totally made of metal and has proven to be indestructable, plus easy to clean and disinfect, so I think it has paid for itself.
The basic design feature which they claim makes it squirrel-proof is the weighted feeding tray - it just shuts if something too heavy gets on it. But on mine, the squirels never even make it to the feeding tray - they just can't get on it at all. The one I have has a more rounded, sloped top than this picture, and being metal, it's slick, there's nothing for them to cling to, so any time they climb on top of the feeder, they just slide right off, on to the ground. It's a great deterrent (plus that can be very entertaining). I have it hanging in the middle of the yard, from a shepherd's pole, so there's no jumping and landing on it from any tree. These types of feeders have been around for many years. I can attest to their success!
I have used the cage-type feeders, which you can buy fairly inexpensively, but the squirrels figure out how to hang on them so the feeder tilts and seed falls out -- until the thing is empty! I even had a cage version where the squirrels figured out how to undo all my lashings on the latch at the top, opened it up, and then just scooped the seed out like ice cream from a bucket! Squirrels are nothing if not terribly smart. Plus my birds all hated the cage-type feeders. They were very intimidated... I can only assume that the "bars" of the cage might keep them from making a quick getaway from the feeder.
The other squirrel-proof choice in my yard is a metal-mesh thistle feeder that the goldfinches love, and which my mobs of sparrows only occasionally bother with. The squirrels ignore it - both the design and the seed turn them off.
Good luck to you!!