Using Galaxy S6 AT&T for data only in Japan

Sorry, I know there are a bazillion posts on this topic but they are all confusing as hell to me, and most of them don't fit my exact requirements.

I'll be in Japan for 22 days next month. I use AT&T with a Samsung Galaxy S6 in the US. I want a data only plan in Japan, mainly to use for navigation (with pre-downloaded Google Maps, GPS, etc). I don't care about texting or calling. I might also need the data for general web browsing to look up info on sites.

I'm assuming it will be cheaper and more reliable to get a SIM card in Japan. I am in the process of unlocking my phone. How can I be sure my phone will work? What would be the better option? SIM card, pocket WiFi? Rent a phone?

I understand your confusion so i will share my experiences with you. ;-)

A good site to check if your phone will work is
https://willmyphonework.net/

Just enter your phone details and Japan as the country and it will show you if you can use your phone. As for a sim-card i have used

https://www.sakuramobile.jp/

many times to complete satisfaction. Nice English website and support. Various data plans and sims with adapter to fit all mobile phocnes. They use the Docomo network which has excellent coverage and good speeds. Hope this helps to get you going. :-)