It sounds like the PH would fit your needs. But, I think you should go with the Tivoli. You have to go with your heart and it certainly sounds like you love the Tivoli. You can get it and if you find it to be too large there is always the option of returning it and picking up your PH. Or as you mentioned you can get the Tivoli GM now and snag the PH at a later date.
Best of luck - both are fabulous bags.