Always had two plus dogs in the house and as above keep each other company and become inseparable etc. Big thing to look out for you though is breed and space!
Dobes are brilliant dogs but if yours is male I wouldn’t get another male as they can be same sex aggressive in territorial environments.
Also two big dogs together when young are like a tornado as they will play for hours and the attention will disappear from the family. Nothing wrong with it as it stimulates intelligent dogs like Dobermans but having the space is a bonus!
StefMcdef – Have seen quite a few rescue working dogs coming in from central and eastern Europe such as GSP’s, Viz etc.
If looking at a HPR breed just be aware that the prey drive will be through the roof due to there upbringing (European training methods can be quite full on!!) and have seen people get into difficulties with them if they have little experience of trained working dogs. The charities are normally pretty good at helping you though.