Always get two, or better, three (like it has been said, if one dies, you may not be able to find one of the same age)
Chickens are social animals and, especially chicks, want to have at least a friend or they will feel very alone and suffer really badly.
Plus a single chicken (especially if young) integrated in a new flock will be picked on very badly.
I once had to raise a single chick (mother and siblings died overnight), here there are no shops that sell chicks and it was during 2020 lockdown so it was forbidden to leave your house, except for very essential needs. Luckily I was home 24/7 so she had company everytime, but it wasn't the same thing, they need company of their own specie. I'll tell you it was very hard. A thing is to remain with a single chick for major cause (only one hatches, all the others die, etc.) and you really can't find any chicks the same age, another thing is doing it on purpose.
If you don't want that many chickens you can raise 3 or 4 and sell the other 2-3 (better if in group so you are sure nobody will be kept alone or will have troubles integrating in the flock) once they are fully integrated in your flock.