I highly recommend the leather liners with Alfie's sensitive skin, especially if the red is your top choice. I put them on the more stiff colors for my girls, and it totally fixed the problem with it rubbing the armpits.
Once the leather softens up, you'll probably find you don't need them, but they are easily put on and removed (velcro), so you could transfer it to another Buddy Belt should you get the itch for another and need them for another breaking in period.
Buddy Belts Harness Liners