Hi Richard,
The straw bales could be a very good option for you. And yes, the heat is a real issue, but it is something you can overcome, especially if you can keep moisture on it.
For conditioning, although I used blood and bone meal, you might get better results by peeing on it. And its cheaper too. Urine is an excellent fertilizer, but it can be a bit hot. If you can get the urine to start breaking down the straw, you can mitigate this problem.
That said, I would still work in some manure if you can do it. My reasoning is that the bacteria from the manure will happily add to the microbe party taking place in the strawbale. They will probably make it break down faster as well. When I use the manure, I worked in in on the sides and especially in between the bales. Basically I was trying to get microbial action going everywhere I could.
Regardless of how you get the nitrogen on the bales, they will break down--surprisingly quick. I doubt that they could survive to work another season, though you could use them as a base on which to set new, fresh bales. This would add yet more microbial activity to the new bales.
But for my purposes, I like just add this decomposed straw to the garden bed as a sort of mulch--and a very fertile one at that!
Good luck on your project, please let us know how it works out!
Eric