If Black Forest area is a consideration, check out Titisee. How far that is out of your UK to Morzine route depends where you’re crossing the Channel/North Sea. We use Hull-Rotterdam/Zeebrugge and distances/timings work well: Morzine/PdS-Titisee and Titisee-Zeebrugge both comfortable day journeys even with young kids.
Quite touristy but plenty non-biking to do. Lake’s good for paddleboarding, etc. Nice traffic-free walking and cycling. Badeparadies Schwarzwald huge indoor/outdoor swimming pool/waterpark complex. Todtnau 25mins away has a bike park with uplift if you feel the need, mountain coaster etc.