You have exactly the same issue as me. I cannot wear Chisel 1 or 2 lasts. UK9.5 is my true size but the same size in Chisel lasts is too small and UK10 is too big. Soft square and Hawksbill works in UK10 works for me.So you think Soft square and Chisel 2 last (same size) instep would be similar ?
And yes, it is very costly to ship back via DHL to AM. My return of a Chisel to change to a Soft Square last costed more than US$250. DHL still make me pay for taxes for returns to Italy.
I think Soft Square with a half a size up will be a rather good bet. Good luck!