Polaroid transfers with currently available materials are cumbersome and unlikely to work well for a travel journal. You'll need to be in near darkness within 30sec of snapping the picture and then you'll need very specific paper (unsized) to take the transfer. You may be able to find a book with unsized paper but if you're traveling you don't want to have to find near darkness to make the transfer every single time you take a shot.
The instax mini is very affordable, looks good, and seems to me it would work really well for a travel journal. The instax wide produces bigger pictures than the instax mini but may be bigger than what you want to travel with. I would steer away from the z2300 and 300 from what I've heard.