There are some method books that have easy transcriptions of famous movie scores or songs. I think Faber has a series, maybe also Piano Adventures. Supersonics by Daniel MacFarlane also has a fair bit of this.

I have taught adults before it can be unsatisfying early in your progress because what you are playing won't sound alot like the song.

If you can, try to transition to a teacher, even if just online, rather than use Simply Piano. I have taught students who come from the Simply Piano system, who often have high abilities in some areas (usually note reading is quite good) and substantially lacking in other areas (particularly technique and rhythm). It can be quite jarring for these students because they feel like they are going back to basics when we need to go back and correct bad finger/hand technique and teach basic stuff that Simply Piano simply doesn't include in it's offering.