Tom and I have been playing with the same Country band for 10 years. I'm on rhythm guitar, he is on electric bass. The rest of the story; Tom has been playing the organ at a nursing home each Thursday for years. The organ died so he started playing rhythm guitar and accompany his vocals. That was going fine, however, he needed a bass to back him up.
So..... I'm on bass and he is on rhythm guitar. Switching from rhythm guitar to bass was easy enough. R-5 came quickly. Chord tones followed so the basics of how to play bass also came quickly.
www.studybass.com was/is a great help. Same kind of songs with both bands so grabbing a I IV V and changing with the chord changes is the same on bass as rhythm guitar, I'm not strumming the chord now just using the chord's notes and building a groove. Augmenting Tom's vocal and comping laying down a steady beat.
Playing well, now that will take time. Yes we old rhythm guitar guys fill our bass lines too full of stuff.
Am I happy? Yes. I still play rhythm guitar 4 to 6 gigs a month and then bass each Thursday. I enjoy both. I also enjoy keyboard, clarinet, sailing, sculling, exercising at the gym with the other grey headed guys and gals, ham radio and the Kiwanis Club. Retirement is great if you have enough toys.