So, I went up with a different instructor today, and explained to him beforehand that I was getting frustrated and didn't really know what it was I needed to improve on, so we had a good run through the circuit in the briefing, talked through what I thought I was getting wrong and how to fix them, and proceeded to do pretty much the best landings I've done.
Upshot being that he thinks that if the wind is calm enough next weekend (15kt crosswind today) then he would hope to be able to get me solo, and if it's windy we'll go off and do a navex which he's given me a route to prepare for. So definitely feel more positive about the whole thing having someone who seems to be actively managing things better!