Assistance on 115 speaker choice

Hello,
I was active on this site for a few years several years ago. I have been idle but am back in!
I am trying to select a 15” speaker for my stand alone 115 cab. It is 3.8 cu ft, dual 4” rear ports, no tweeter and has minimal batting.
I have run several tuning calculators and have come to the conclusion that without experience and knowledge on how to read the graphs and what they relate to regarding actual sound on stage, it is a guess as to what will work best.
I’m looking for classic deep, smooth non mid extreme bite, think Motown sound.
I play a Pbass through a TC BH500 head. Neo would be best for my aging back.
Any help and explications as to what speaker and or port tuning/length would be greatly appreciated.