I'm having trouble with my current pack, either because It's not the right size for my torso, or..
What pack do you have now?
Most larger bagpacks have adjustable parts for your length.. sometimes there are a bit hidden underneed the pads tho.
Also it takes a bit of practise to walk around with a bag.. how to load it, devide the weight vs reaching things easily. How to adjust all the straps.. (length, shoulders, waist)
I had an external one. 2 trips , 2 different bags. Both short hiking trips.. never again. Hated them. Couldnt find the proper way to put it on.
I swear by internal frame. More flexible, easier adjustments. Softer. Not always better aircirculation between yr back and the pack tho. (Cheaper once usually have less circulation.
Wouldnt mind trying a new external frame once.. but the 2nd hand stuff you find is all crap in my opinion.
My favourite pack was an haglöfs from 8 years ago. Borrowed itfrom a friend to walk across iceland 2 summers ago. skipping, jumping, climbing,.. no problem.. tried buying it from my friend but she loved it too.
It was a womens. Meaning the hip part is slightly different but it fitme perfect. As a lot of other packs slide down my waist cause i am skinny. ( this one rested on my hips just perfect cause the shape.
Keep playing around with all the straps untill you find the most comfy possition. If nothing else works check out a new one..
If you buy a new one its Better to spend a bit more money on one that fits you perfect then buying something cheap. Walk into all outdoor stores, try em on. Ask to put weight and volume in em .. especially if you are gona spend a few 100 dollars you want to have something that wont hurtor annoy you..
A few 100 dollrs is a lot of money if your homeless.. but its your everything..
And you can just try em on in stores and find something you love. Then try and find them online 2nd hand