You mentioned considering a left-hand IWB holster due to your back issues. That makes sense, given your past preference for 4-5 o'clock carry isn't working out anymore.
Left-hand IWB could be a good fit, especially if you're not too concerned about the extra draw time. Since you mostly wear shorts and T-shirts, you might want to look into holsters designed to minimize printing. Some folks also find that a slightly different positioning or a holster with adjustable cant can help with comfort and concealment.
Have you thought about reaching out to a local firearms instructor or someone who specializes in concealed carry to get some personalized advice? They might be able to offer some tailored suggestions based on your specific needs and preferences.