Η μαμά μου συνήθιζε να βάζει λίγο βούτυρο στη φρυγανιά, αλλά εγώ προτιμώ μόνο μαρμελάδα.

In normal Modern Greek, the unstressed possessive μου usually comes after the noun:

• η μαμά μου = my mum
• το βιβλίο μου = my book
• οι φίλοι μου = my friends

So η μαμά μου is the standard word order. If you want extra emphasis, Greek often uses δικός/δική/δικό instead, for example η δική μου μαμά.

Yes. μαμά is the everyday word for mum / mom. It is warm and natural in speech.

A more formal word is μητέρα. So:

• η μαμά μου = my mum / mom
• η μητέρα μου = my mother

συνήθιζε is the imperfect form of συνηθίζω.

Here it means something like:

• used to
• was in the habit of
• would typically

The imperfect is used because this is a repeated or habitual action in the past, not a single event.