For goose down pillows, I'd suggest getting a dual chamber (there's a smaller core pillow in the middle) for neck support. You can get them at lots of places like Linens N Things, or the Company Store... There's a picture of what I'm talking about at the Company Store website:
http://www.thecompanystore.com/paren...dept%5Fid=3501
Also, forget the firmer-is-better-for-your-back "rule". It's leftover from the last century (before manufacturers began stuffing as many springs as possible into mattresses). If you're looking at a mid to high end mattress, you should be comfortable from the minute you lie down on the mattress. If you're not, forget that one and try another.
Elec: I don't know about that extra width (though I imagine the answer depends more on your physical stature than anything else), but I would just point out that if you like to bargain shop for sheets, non-standard sizes (XL Twins, California Kings, etc) are harder to find. I like to get my sheets from discount places (ABC Carpet & Home outlet, Homegoods, etc) since I'm perfectly happy with "last season's" sheets.
Not to go on for too long about bed sheets, but if you're spending significant amounts of money on a mattress get good quality sheets! You can find decent sheet sets at Ross/Marshalls/Homegoods/whatever for around $40-$50...or you can always step up and take a look around at the real goodies from a range of companies: Pratesi, Frette, Anichini, Sferra, Porthault, Yves Dolorme, etc. I'm a big fan of real linen sheets, but they're wrinkly (charming), and expensive (not charming). Also, avoid the "hotel" lines, they're ridiculously overpriced (I'm talking to you Frette) and anything with polyester in it.