I enjoyed Wasona a lot. Official books are not really needed.
kama sona pi toki pona la jan @violet o kepeken ilo ni:
• open la sina o lukin e lipu Wasona. https://wasona.com
• ilo Wikipesija li lon toki pona a.
https://f-droid.org/packages/org.wikipedia
• ilo Sikule la sina ken sitelen kepeken sitelen pona.
https://f-droid.org/packages/com.blacksquircle.ui
• mi wile sona e nimi la mi kepeken lipu Nimili. https://nimi.li
@violet I'm always going to recommend https://www.youtube.com/watch?v=j_a0s0wowhE&list=PLwYL9_SRAk8EXSZPSTm9lm2kD_Z1RzUgm&index=1
And https://jamesmoulang.itch.io/nasin-sona-musi does a good job of gamifying the writing!

@violet I personally took jan Kekan san (Gregdan 3's) course which is on youtube and his website (mun.la/sona)
o kama sona pona!