The trouble is, whilst I accept there are some circumstances in which WiFi is the only realistic compromise, it can be difficult to know whether you are dealing with a WiFi problem or a DSL one. The fact you say all was well in your old house may be consistent with a WiFi problem, because different houses are built of different materials, and different houses have different neighbours who may be competing with you for the WiFi spectrum. I have a 54g home network, as well as a wired LAN. Video distribution doesn't really work for me over WiFi, it needs the wired LAN. That's usually around 10MBit/s, which is not much more than you are trying to push through your own WiFi.
If WiFi is found to be the problem then one long term solution might be homeplugs. I've never used them myself and personally I have some reservations about security, but plenty of highly respected forum members speak highly of them so I suspect they are absolutely fine. But they would also be quite an expensive experiment and, as we don't know either WiFi or DSL is causing the problems, there's a chance they may not help your specific problem.
Is there any chance that, even as a temporary measure, you could connect via ethernet just to see if the situation improves? Options would be (ugh!) move the PC closer to the phone socket, or borrow a nice long ethernet cable that you can temporarily trail through the house? Another experimental option might be a long phone extension so you could move the router temporarily upstairs, but you'd need to keep an eye on the DSL stats to make sure the extra wiring doesn't degrade the DSL.