I'm considering the same for https://pwpush.com. Currently on paid Heroku ($59/month) with a lot of traffic.
DO App Platform is better than last year but still a bit quirky. I haven't found a better alternative that is more 1) mature, 2) reliable, 3) paid/supported, 4) enough features.
I've been waiting to make this same move but holding back because DOAP isn't quite as featureful yet, e.g. not supporting scheduled jobs, which for some reason ALL my Heroku-based projects use in some way.