This below video shows you a four chord progression in the key of C major using one borrowed chord Gmaj7th just to add some colour. The chord progression goes Cmaj7th, Gmaj7th, Fmaj7th, Emin9th. This would normally be in the key of C Major except I have substituted Gmaj7th for G7 which would be correct if it were all in the key of C major. I purposely did this to add more character to the overall sound. Also notice that the final chord E Minor is using the 9th key, which is a black key and also outside the C major scale.
The trick here is to avoid the Dominant chords if you want the RnB or Neo Soul sound. Switch the Dominant chord to a major for a pleasant soulful borrowed chord. It is never a problem using the Dominant or 7th however it can make the overall sound a little more commercial or pop sounding. However if you have the right singers e.g. Boyz II Men from the 90s, popular or typical chord progressions can still sound soulful, however this below is a good method to get obvious soulful sounding chords.
Tip: Also try a Gminor7th instead of a Gmaj7th for a new sound.