I'll be taking an open ended cycling trip soon, setting off in the morning without much idea of where we'll be spending the night. Although both T and I have internet phones, it's we've decided to take accommodation booklets - strangely old fashioned though it now seems to use directories printed on paper - wow!
Strangely enough, it's often easier that way. I've had about enough of peering at a tiny screen and desperately trying to coax a feeble internet connection in faraway places, and it's particularly tiresome if it's getting late and you really need to find somewhere but your phone gets slower and slower or just packs up
We cycled from London to Scotland a few years ago and the two directories we found most useful were the YHA Handbook and -Bed and Breakfast Nationwide.
Youth hostels are good places to turn up if you are on a bike. They are geared to people doing outdoor things, they have secure bike storage, you can clump around in outdoor gear without feeling stupid and sometimes meet other cyclists or walkers to compare notes. You often have the choice to cook your own food or get a meal made for you on-site. And they're also the cheapest option - and these days, hostel accommodation is usually comfortable and convenient. The only downside is that you have to be a YHA member to get the handbook, but since you generally have to be a member to stay at hostels, too, that's not too bad really.
Bed and Breakfast Nationwide has a free booklet (for 2 first class stamps) and their properties tend to be reasonably priced but pleasant. Unlike some other b&b guides, their properties aren't usually quirky historic houses with knot gardens and private fishing, and the owners may not be polymaths who speak 5 languages and bake their own croissants ... but we've nearly always found them comfortable and convenient.
Anyway we're heading to Wales this time, so I hope that the properties in that direction are as good as the ones we found going Northwards.