i use whole buds and thats about all there is to it! also i treat it gently enough that it doesnt become any softer. if too much heat is applied to oil it will soften considerably. usually softer oil is the result of using trim or ground up material to make oil with. the finer your material you extract from(barring it being 100 percent trichomes) the darker and runnier your resultant extract.
I,on the other hand,use all trim most of the time,and it takes the resulting oil about 96 hours to harden (still,always less than the Amber Grade) when using well-ground trim.
Like HMK said,when you use all buds you get that gorgeous Amber Ice that's quasi-portable....
Occaisionally I get a wild crosshair and make a batch that way,for the 'Amber Ice',but mostly I ustilise small buds and trim for my bubblehash and oil-making.
My program....is to use every last bit of processable tHc-
....It's an efficiencey thing,you understand....and it's all great oil,just different.
One neat thing about oil,it can be laminated inside cards and carried anywhere.
Just freeze for a minute,cut open,and peel back the oil.
Simple.