When I started writing songs it was on bass guitar. I'd sort out where the bass went, the lyrics and a vague melody. A friend would match the bass with chords he liked. After I learnt an half dozen chords I played the ones I could to match the bass. When I learnt a few more chords...basically nine...I'd sketch with guitar & add bass. I learnt them becasue they were simple...Em, Am, G, D, Dm, C, Bm, F & Fm. No sharps or flats obviously and the were, for the most part, simplified three note versions of the chords. I knew nothing of keys, 5ths etc. so winged it and came up with some okay songs. A little later by ear I worked out variations of those chords and came up with things like Am7 -> D -> Dm -> Am -> C -> Em -> then A2 "resolving" to Am as the base for a song. Those any many other variations stood me in good stead until I found I needed to sing my own songs through lack of singers willing to do so - I was helped to find that A was the key for my voice, weak, thin & limited and I learnt the extra chords necessary to accommodate that, (mainly taking the open F & D shapes then moving them up n down the fret board.
With BIAB it's even easier to add nice chords to a bass progression. Work out the bass, drop what you think are the roots into the chart bars and then tweak the chords to taste. Don't feel you HAVE to follow the theory stuff...if you like where your bass is going work from it...here's more freedom that way.
I was willing to do that slow evolution across almost 50 years but I can understand someone being too impatient for that.
Enjoy the learning.

Last edited by rayc; 08/11/22 12:29 AM.
Cheers
rayc
"What's so funny about peace, love & understanding?" - N.Lowe