As for where to buy it in Europe, I'm afraid I can't help there as I'm in the US. Hopefully someone else will answer that for you. Perhaps you have ebay or Amazon accessible in your region? I'd check those first. If not maybe a local computer store may have it.
I would probably get the 4GB model. Most of the OS versions for PI are 32 bit, so there is no benefit in more than 4GB. With more RAM, the GPU can have more RAM.
It is expensive, but, after having SD cards fail, I have converted both my PI4s to M.2 SATA SSDs. 10X the performance and much higher write endurance.