I just bought a motorized Reality switch, see this thread, that I am going to try on Iris. It works great on smartthings, so if it doesn't work, I will put it on a switch in the house and connect it to smartthings.
The other switch mentioned in the linked thread is a Z-wave version, I would try it as well, but it is limited to none ganged switches if I read it correctly. The Reality switch can fit on a ganged switch box with no issues. I have three of them now I use on smartthings and they work great, as I have the same issue as you in my house. I think I am going to have some runs re-wired so I can use smart switches but in some places I will just use these.
You can use Hue bulbs or Lutron switches. But both require you to use their hub and link the accounts to Iris. The Lutron switches advertise not requiring a neutral wire.
I use the Hue bulbs in several places, even using an Iris motion sensor to control a couple and an Iris contact sensor to control others. All of my scheduling is through Iris, and I rarely even open the Hue app.
I don't have any experience with the Lutron stuff, just providing the info based on their advertising.
The Osram Lightify bulbs pair with the Iris hub and no additional bridge is needed to pair them with the Iris hub like the Hue and Lutron lights. They are also substantially cheaper than those mentioned but unfortunetly eBay is the only place I can find them. Sylvania also has a flood light that can directly connect as well. These bulbs can be turned on, off or dimmed.