I have been using focusmate which is not advertised as being for ADHD, but it works great for booking "focusmate" sessions that are like body doubles. You can schedule a session at any time, there almost is always somebody to pair with you. Website is focusmate.com.
I just googled "body double app" and got a lot of results. I might try one of these.
If you have experience with a body double app, please reply.