I have a small collection of Easy Guitar books recently acquired from used book stores and the internet. Hal Leonard has produced a large collection of them in various genres. The reason that I like them is that in their "simplification" they tend to be tabbed on the DGBE strings and there are also not just single note melodies but harmonic dyads and 3 or 4 note chords. The books are in both musical notation and tab.
Two books that I think would be appreciated are Beatles collections. Since the melodies are world reknowned it helps the learning curve. Although there are songs that are strictly in guitar tab, and would require some thought to adapt, there are also some that are purely baritone uke ready-to-play. Both books are for the beginner / intermediate players. I found both used at half-priced books.
The Beatles Classic Hits
Bari simple tunes -- Hello, Goodbye, Help!, I Saw Her Standing There, If I Fell, The long and Winding Road, Nowhere Man, Something, We Can Work It Out.
From Liverpool to Abbey Road (Learn to Play Guitar)
This book has a very bari version of Yesterday, I Will, No Reply, Carry That Weight.
Some of the other songs in the books may have notes on the E and A strings of the guitar but since the baritone has D and G strings I may play the E-string notes as a D-string +2. I do something similar moving the A string notes to the G-string. The problematic note for me is to obtain a low C. Sometimes I play the C chord and other times I play the C note DGBE=xx1x.
e ------------- e ------------
B ------------- B ------------
G ------------- G -----3--0--
D ------------- D --2--------
(The notes are E, A#/Bb, and G)