Hi Hansi,
I’m sorry you lost one of your birds. Ideally, try to find a bird that is a bit older like the one you have. The problem is, if your remaining bird is a male, you really shouldn’t put a female with him unless she is 2 years old or older. The reason is that the older male may decide he wants to breed and a young female shouldn’t start laying eggs until she is about 2. When they are younger than that, they really are not fully developed physically or mentally. The other option is get another male, and then you won’t have to worry about eggs. Two makes can get along just fine. When you do get a new parakeet, keep it in a separate cage across the room or in another room for about 30 days, to make sure it is healthy. Then you can put the cages side by side so they can get to know each other. If they start sitting near each other and interacting through the cages, then you can try them in the same cage. Always supervise them closely at first, and make sure you have at least 2 food and 2 water cups across the cage from each other so one bird can keep the other away from food or water. A little bit of squabbling is normal but if there are any feathers being pulled out or blood drawn, you need to split them back up. But generally they will get along.
Thank you for asking Lafeber,
Brenda