Before you make any hard decisions about what to buy (if anything) go find a bass instructor - even just for one lesson to get some critique on your playing angles and strap length. Plenty of people your size can play a long scale bass without pain. It's most likely a technique correction. You should at least post a picture or video of how you hold it so folks here can offer suggestions based on the actual issue, not on how we imagine it.
Re: 5 string - go for it - it doesn't take long to adjust especially if you don't have a lot of muscle memory on the four string. If nothing else, it will help you with your reach issues (can play most first position stuff on the 5th fret). But if you're considering it for jazz purposes, it may mean solo work and a lot of bass soloists types prefer the high C (EADGC) tuning to the Low B (BEADG) - and that won't help with your reach.
I really think if you fix your position on the bass, your pain issues will go away. And BTW don't keep doing something that causes pain - you could cause further damage that won't heal properly.
Re: 5 string - go for it - it doesn't take long to adjust especially if you don't have a lot of muscle memory on the four string. If nothing else, it will help you with your reach issues (can play most first position stuff on the 5th fret). But if you're considering it for jazz purposes, it may mean solo work and a lot of bass soloists types prefer the high C (EADGC) tuning to the Low B (BEADG) - and that won't help with your reach.
I really think if you fix your position on the bass, your pain issues will go away. And BTW don't keep doing something that causes pain - you could cause further damage that won't heal properly.

(no i didnt read them all)