The perfect compromise
After weeks of research, I've settled on this 43QLED780 TV from TCL, which has the latest technology and, above all, excellent connectivity (Bluetooth, Airplay). While other brands are very interesting at first glance, their OS (e.g. Vidaa) seems rather limited, and Google TV offers some significant options such as Cloud Gaming applications (NVIDIA GeForce Now or Shadow). For a first TV when you're not an expert, it's quite frankly the best I've come across.
The "Versus" site for comparing TV specifications was enormously useful.
Close to a gutted bay, QLED technology is really necessary, and 4K is a real joy on streaming, or Youtube. The sound is really good, but like many Smart TVs, you have to adjust the sound for each application (Disney+ and Netflix) or each film, but that's a limitation common to all TVs, they also adapt the sound when changing films in cinemas!
PS: Don't trust the online calculators (e.g. Samsung's) when it comes to choosing the right size of TV for the distance, because if I'd followed them, I'd need an 85" TV. I watch it from 4 metres away and I can assure you that it's perfect, especially in bed.