Fixed price works for some projects and not for others. I like fixed price for self-contained projects, and you can reduce the chances of big surprises by charging for a discovery/design phase before you quote for the development. I find fixed price less practical when there's multiple designers/devs involved though, when you can't control the decisions and scoping as much. Sprint based pricing can be an option here.
Besides hourly, have you tried daily billing? I rarely see this mentioned but I think half day billing works well: unlike daily billing you're not forced to work the full day for one client, and the timekeeping can be less granular so you can focus more and worry less about eating/explaining hours.
I've seen people advocate weekly billing (and even monthly), but then what if you can only commit to a few days some weeks?