If I could give somebody one piece of advice about this, it would be about a twelve-dollar cable, and I would say it before anything about services or boxes.
Run an ethernet cable to whatever is playing the television.
That is it. That is the advice. It costs less than a takeaway coffee twice, it takes twenty minutes including tidying it under the skirting, and in this house it removed an entire category of problem permanently.
Here is why it matters more than people expect. Your internet connection into the house is one thing. The connection from your router to your box is a completely separate thing, and it is the one that fails. Wifi at eight in the evening is competing with every device in your house and, in a building, with forty other networks. None of that shows up on a speed test, because a speed test runs for ten seconds and video runs for two hours.
A cable does not care. It is the same at eight in the evening as it is at six in the morning.
Before the cable, we had a picture problem three or four evenings a week. After it, roughly one a fortnight. Same service, same box, same package. That is the entire difference and it cost twelve dollars.
If you genuinely cannot run one — a rented flat, a wall you cannot drill, a room on a different floor — a powerline adapter that sends the connection through the electrical wiring is second best, costs about forty dollars, and is still better than wifi through a floor.
What is not the answer is a wifi extender. I bought one first. It improved the signal strength and not the picture, because an extender relays everything twice and halves the bandwidth in the process.
The full diagnostic order, cheapest and most likely first, is in this guide.
Twelve dollars. Nothing else I have bought comes close.