My local lumber yard does not care white oak to match the wood I have
put has a few 5x5 Ash posts at 6 dollars a board foot or so.

Will this stain identical to my white oak?

I was thinking of making or using 4x4 for the posts. Would this size
look right?

Also, how does a matress and box spring fit in a typical bed? I had an
old bed with an angle iron type frame that bolted to the headboard.
But I see pictures alot of stained side rails on each side. Do these
have any cross pieces that support the middle?

Thanks!

Will this stain identical to my white oak?
No, of course not. It's not the same wood. You might get it close to
the same color if you play with a bunch of different colors of stain or
even mix your own, but the texture and pattern will never look the
same, especially given the distinct grain pattern of oak. In my
opinion it's worth looking around or driving farther to find real white
oak, if that's the look you want to go for. Did you ask at the local
lumberyard where you might be able to find white oak? If there's a
woodworking club or guild in your area, I'm sure someone there could
help you find a good hardwood source.

Would this size look right?
Depends, how do you want it to look? 4x4 would look fine in my opinion
- the bed I'm building has 3 3/8 x 3 3/4" posts, about 37" high for the
footboard and 46" high for the headboard. These things are so heavy
and solid they'll never go anywhere... I wouldn't want to try to move a
bed with 5x5" solid hardwood posts.

Also, how does a matress and box spring fit in a typical bed?
There are a variety of different ways. Look for "Bed Rail Fasteners"
or "bed bolt" at rockler.com or leevalley.com. Of course welded angle
iron bolted to the posts works as well - totally depends on why you're
making the bed and what you want it to look like when you're done.

I'd suggest some good-quality, illustrated plans for a project this
size - I'm using the plan listed below, and below that is a link to a
website someone kindly made of the detailed process using a variation
on the same plan. I'm modifying the plan a little, but there are a lot
of things I wouldn't have thought of if I were completely designing it
myself with no plans.
http://www.rockler.com/product.cfm?page=10721
http://www.uniqueprojects.com/projec...issionbed1.htm

Here are a few other plans I found with quick searches on various
woodworking supply sites:
http://www.rockler.com/product.cfm?p...er=bed%20plans
http://www.leevalley.com/wood/page.a...158,46161&ap=1
http://www.hartvilletool.com/product/11504
http://www.amazon.com/gp/product/B00...lance&n=228013

Good luck,
Andy

Wood Magazine had plans for a bed a few months back that I built. It
used glued up oak boards to create the 4x4 (approx) bed posts. Works
great. They show how to do it so no edges of the boards show if you
want to go that far. The bed uses 1 1/4 inch thick bed rails about 8
inches high. They are very heavy. I used the long angle irons from a
cheap metal bed frame and bolted one to the inside of each rail to
support the mattress. Several wooden slats add support. In addition I
found it necessary to add a center support near the headboard that goes
to the floor to prevent sagging in the middle. When it comes to
attaching the rails to the headboard, you can't go wrong using the
previously mentioned 'bed bolts'. The other mounting hardware I tried
using wasn't strong and stiff enough. The bed bolts make for a very
secure connection. Good Luck