You choose a saint by delving into them.
Go to catholic.org/saints/, there’s a myriad of saints there… If one specific saint seems to appeal to you, dig a little deeper.
Father Robert Barron suggests that you might pick a saint you is similar to your own lifestyle… A mother and Teacher (Elizabeth Ann Seton), attracted to the mystics… Teresa of Avila, John of the Cross or Padre Pio, devoted mother and wife, Saint Rita… etc. etc.
I like the saints that have their own words available to me, such as Catherine of Sienna or Teresa of Avila or the Little Flower, St. therese of Lisieux. I know that reading their actual words is much more illuminating and amazing.
However, my own patron/name said is Saint Anne, mother of the Blessed Virgin. Originally it was because my priest noted my middle name was Anne, and that would be a good patron. That simple statement ended up being the best choice for me without any research or investigation at all.
There’s a ton of Saint books out there as well, Modern Saints (there’s two books of them) by Ann Ball has great descriptions and stories. From there you can investigate the particular saint by his/her writings, if available.
Bless your journey together towards Truth, Light and Easter!