I don't have a Now TV box or USB stick. I stream my Now TV through the Samsung app on my smart TV.
It's looking as though I won't be able to get the Anthony Joshua fight as I don't have the box office app, can anyone comfirm this? I'm hoping someone can prove me wrong!
Welcome to the forum. Sky Box Office Online is a separate service to NOW TV so you won't be able to watch it on your Samsung NOW TV app.
If you order from https://skyboxoffice.neulion.com then without a NOW TV box/stick your options are limited to watching on a PC/Mac or on an Android/iOS tablet/mobile. More details here
The other alternative is if you have a friend/family member with a Sky TV sub you could go halves with them and order through their separate Sky TV Box Office service instead.