erm... sorry to point out the obvious but if you buy bigger size pants and just roll up the bottom it saves buying loads of new nappies and you'll get years out of them as when he potty trains you get to root out all the pants he grew out of that he suddenly fits again!
dd was in cloth in the heatwave of '06 and was happy enough, tbh i tend to strip them off in the house alot anyway and just mop up the puddles but i'd do the same in sposies, if anything they're sweatier as they're all plasticy.
ds1 grew out of MEOS at 6 months and then fitted them again from about 22/24 months until a few weeks ago (he's 2.9). they're body shape changes as they grow and move differantly.
just avoid anything that's fleece lined or microfibre if you're worried about the heat issue.
kissaluvs are lovely thin nappies, i bought a wide variety of size ones for ds2 and of all of them the kissaluvs are the best all round but again, just based on the pants issue i'd go with bigger pants... or if it's a nice hot summer, a nice wrap and no pants at all! wait and se if he does actually grow out of the MEOS, it's hard to predict a babies growth and body shape. (although, obviously if its a case of wanting some pretty new nappies go nuts, lord knows i found excuses to but whole new sets for both my boys )
i'm not keen on wool for daytime.... in fact i've not had much luck with my wool wraps at all... they don't clean well if poo gets on them, dd's all disintergrated from her acid pee and they ooze alot if any pressure gets on them at all.
sorry, that was very rambling, dp is playina video game that keeps distracting me with explosions and stuff!