Translation:My husband was deciding these things alone.
Actually, it is the best tense to use "used to". Il passato imperfetto is mainly used to describe repeated past actions but we don't know the exact time it is not stated.
My mother language is spanish and it is quite the same meaning.
Mio marito decideva queste cose da solo. (Italian)
Mi marido decidia estas cosas solo. (Spanish)
My husband used to decide these things by himself. (They all have the same meaning). My husband used to decide these things in the past but not anymore, this was a repeated action in the past.
If it happened just once you have to use il passato prossimo. Here is one weird thing about Italian, il passato prossimo can be used for the past simple and the present perfect in english, you'll know which of them to used based on the context, seems difficult but is not it is just a matter of practice. Italians has a tense for the past simple that is Il passato remoto but is not use regularly, and only a few people on the south of the country use it.
So to sum up, il imperfetto can be (past continuous, or past using "used to") and the passato prossimo can be (past simple or present perfect).
If you have further questions let me know. Appologize beforehand for my written english, it's been a long time since the last time I wrote something.