Boy, with your husband not giving a hoot about onsen ryokans, and the futon thing possibly being an issue (yes, the better ryokans have more comfortable futons, but some people still have trouble with them, apparently), I'm not sure I'd do it. (At least he's willing to try one, for your sake. Good for him.) August is not a super-duper time for onsen bathing, either, in my opinion.
Hmm. How about just getting a good solid Western-style hotel that has really nice bathing facilities? (The Japanese word is daiyokujo, which means large bath, but there is no good translation in English, and the usual ones such as "public bath" and "communal bath" conjure up unappealing and misleading images. "Spa" doesn't really capture it, either.) There are a lot of them these days (many new midrange hotels are opening up that have these baths, as they are very popular). Then you can experience the whole bath thing, and your husband can opt out if he chooses. And you could get beds to sleep on. Then, go to a restaurant and have a kaiseki dinner. (The combination is certainly not the same as staying at an onsen ryokan, but it has some of the features, without some of the potential drawbacks.)
There is a fairly new hotel in Kyoto that has an attractive daiyokujo and has gotten very good reviews, the Solaria Nishitetsu Hotel Kyoto Premier. (I haven't stayed there myself but have seriously considered it.) Possibly give it a look, or consider some other hotels in Kyoto (or even Tokyo) that have a daiyokujo? https://solaria-kyoto.nishitetsu-hotels.com/en-gb The Solaria Nishitetsu (definitely a chain hotel, but not a massive one) is in a pretty good location, as far as Kyoto goes. Where to stay in Kyoto is a complicated question, but for a couple of nights I wouldn't agonize too much over it (just pick one of the popular areas, either "downtown" or else near Kyoto Station). I can't advise on the higher end hotels in Kyoto as I don't have much experience. I did have a lovely stay at the Westin Miyako quite a few years ago but they were discounting much more generously back then. The room was comfortable but nothing special, aside from being a generous size. The location is somewhat inconvenient and there aren't a lot of places to eat in the immediate vicinity. On the plus side, it's walking distance to a number of very nice temples and other places. I also had a nice stay at the Okura. I would say it is comfortable and reliable but nothing particularly special (and definitely not boutiquey). In the Kyoto Station area, if you want a "public bath", maybe take a look at this new place: https://www.hotelvischio-kyoto.com/en/
. I had it booked for my last trip and was looking forward to it but my plans changed, so I haven't tried it yet. This is a moderately priced hotel. A more expensive one that is also brand new and right next to Kyoto Station is The Thousand Kyoto. https://www.hotelvischio-kyoto.com/en/
It is out of my price range, but looks nice. I haven't seen any reviews.
Well, I don't envy you, having to hurry up and make all these decisions. We typically spend months agonizing over our itineraries and booking hotels. But at some point you just have to make your choices and then don't look back. I'm sure that whatever you come up with will be great.
One more comment is that although many people will tell you that you are spending too much time in Tokyo, everyone is different and with all the day trips you have planned, you might end up wishing you had even more time there! So don't overthink that. There are so many things to do in Tokyo that you could spend a month there. And sometimes it's nice just to do some low-key things like walk along the banks of the Sumida River, or have a really nice lunch somewhere and have that be the high point of your day.