I'm so sorry for your loss, Nicoise. I wish you peace to find the more beloved memories of your mother.
When my grandfather died, I was so lucky, I found the birthday card he and Grandma sent me when i turned 18. Grandma told me he'd picked it for me, which surprised me so much: it was rimmed with pink and fluffy feathers! From there I remember when I spent the evening of my 21st birthday with Grandma and Granddad, and made a small roast dinner and ice cream sundaes with them.
(I wrote these memories down, because maybe they could jumpstart your search for some nice memories.)