2:05 p.m. on July 17, 2012 (EDT)
There are a few ways to lower your shoe volume with inserts of different thicknesses.
You might be able to raise your heel a bit with 'heel lifters'.
These add more to the cost of the shoes you already have and don't necessarily provide a good fit for your feet.
Here is a primer on finding size of foot.
http://shoes.about.com/od/fitcomfort/ss/measurefeet.htm
REI has a training class for boot fitting. I'll give you a bit of what I saw the last time I got boots from them. I was looking for more support, one that could use crampons, and for heavy off trail use.
She first spent time with the Brannock device. First sitting; then standing (to see spread); then on one foot leaning to the side; then the other. She looked at my bare foot for wear patterns and deformities and pushed a few places asking if that was tender or 'felt differently' from other places she poked. She picked out the problems I had (foot stepped on by a horse, pronation different on one foot than other).
She picked out a few boots in the type I was looking for. Slipped them on tied them up and then pointed to different parts of the boot to see if I there was a problem. If while pushing I felt something different or odd, she would trade shoes and see if the same thing happened.
Having picked the best of the litter, I was to spend half an hour wearing them in the store (the idea is to get me to spend more eye time on the goodies, I suspect). I returned to get her to do more prodding. She put on another pair of socks (having two on already) and had me determine if anything significantly had changed.
What she was looking for was if the bend of the sole of the boot matched where my joints bent, if I could wiggle my toes ('needs enough room to play piano'), if there were any points of boot that seemed to be pressing on flesh more than any other place.
Off with the third pair of socks and the boots felt roomy enough. She pushed on different parts of the boot to see if I could feel her thumb and then would mark them with scotch tape. When she had finished with her assessment of the boot and my feet and agreed on 'hot spots' to be, she moved to a boot anvil.
The tool looks like and extended 'S' attached to a very heavy base. She put the boot over the anvil with the pointy rounded part inside against areas she had marked with the tape. Then she 'massaged' the boot from inside with some slight pounding with a leather mallet where the tape was. Then moved to the next one and so on with the other boot.
I walked out with a pair of the most comfortable boots I have worn right out of the store. I use them with my inserts. Never a blister or injury from them.
You should be able to get a good fit with somebody who understands what kind of a boot that should fit you. Boots are the main thing to spend more money on. The boot should fit the types of hiking you will be doing as well as your feet.
Be very careful with mostly fabric shoes/boots. There is a danger that you will tighten the lacing and reduce the toe volume. You have a risk of getting Morton's neuroma with shoes with little toe room. Not fun!