>>> Used to your average zinfandel or sauv blanc
How about a decidedly above average Sauvignon Blanc?
I tried a bottle of 'Truly Irresistible' Leyda Valley Sauvignon Blanc from the Co-op recently and I was extremely impressed with it. It's got a lovely sharp (but not aggressive) taste to it, somewhere between dessert apples and gooseberries. It cost £7.99 but was as good as some wines that I've paid two or three times that for.
So I googled it to see if others agreed. I found that it was recommended by both The Guardian
https://www.theguardian.com/lifeandstyle/2015/oct/18/good-with-wine-co-operative-review-david-williams
and The Telegraph
http://www.telegraph.co.uk/food-and-drink/wine/susy-atkins-why-the-co-operatives-truly-irresistible-wines-are-e/
Otherwise, for a quality white wine, I'd suggest seeking out a white Rioja. Such wines are traditionally made from Viura grapes but many vineyards have been replacing Viura crops with grapes which produce higher yields, so the rules now allow white Rioja to be made with a minimum of 51% Viura and up to 49% Chardonnay or Sauvignon Blanc. Waitrose is a good source of white Rioja wines (which can be difficult to find in many other supermarkets) but their website is currently offline, so I can't point you towards any particular one.
A further alternative might be a
decent bottle of Chardonnay, which means one from a region which is somewhat cooler than the high-yield areas where most Chardonnay grapes come from. The obvious region to look for there is Chablis, which produces some lovely wines.