Translation:We talk of moms and I obviously think of mine.
I think that your translation is actually much more fluent. Maybe not literal enough.
The prepositions with the verb "pensare"
"Pensare A qualcuno"
"Pensare DI fare qualcosa"
Therefore "pensare alla mia (mamma)"
The difference is the same as in English: "mom / mother" - "mamma / madre". So it wouldn't be entirely wrong, but not entirely correct either.
"Mine" is a pronoun, so it takes the place of the noun. "She's my mom" or "She's mine."
How would you say "I obviously think of myself" in Italian (if I am a mother too and talking about moms makes me think of me)?
Think of "la mia" as "mine" not "myself." I think "mi stesso" is myself.
The British English equivalent of Mom is Mum which I think DuoLingo accepts.
Donpp might mean that the plural sounds unnatural. I think I say "moms" out loud on occasion, but it looks strange written down (as a native speaker).