I think Ireland is probably an example, where the number of representatives per district ranges between three and five, so that there are some districts that are in fact closer to being a one-member district. I don't have this at my fingertips and would have to look it up, but I also think that in Switzerland most of the cantons elect representatives by proportional representation, but a few smaller, very small, cantons have just a single representative. If you have a single representative, you necessarily need a majoritarian system, but not necessarily FPTP. You could use the alternative vote system, which also works with voter preferences. That would be my recommendation if it becomes impossible to have multi-member districts and you need a few single-member districts, that is, if you're going to use STV, which is a preferential system, to also use the preferential system for that single-member district, which would be the alternative vote.
On August 22nd, 2016. See this statement in context.