I think Aldi & Lidl are either for those who aren't too bothered, or for those who really know their stuff. Co-op is a bit more reliable.
We are very lucky with a local wine merchant who know they won't survive if they don't look after their customers. We get almost all of our wine from them £6-9 a bottle unless we are pushing the boat out, and all good. Shame yours isn't more sensible.
I would certainly ask your friends for advice "what would go nicely with......"
If you can be bothered, the weekend magazines tend to review wines, so you could pick up a hint or two. Otherwise I would go to a 'good' supermarket and pay £8-10 a bottle. You probably won't get a bargain, but it won't be duff.