Something I noticed, virgin supply you with shoes every 9 months. On average, my shoes lasted a maximum of 6months at other airlines where I was required to buy them (they were a tax deduction).
Within 6months keeping in mind, they were the victim of countless carts savaging the exterior toe, various surfaces from the wet winter tarmac in sydney to the hot extremes of the Broome tarmac in summer. They copped a beating.
Have 2 pairs per 6 months, and alternate. Don't wear your crew shoes out (yes, people actually do!?). All the other suggestions are valid. My best suggestion - visit a podiatrist. Have them scrape your feet, and look at getting your 'foot health' in order. If you have private health cover, its a very cheap exercise.
With some good shoes, some good orthodics, and a regular inspection and treatment of your feet, you will feel much better at the end of 12hours on your feet.
As for worrying about the smell, to be honest, i never found anyones feet smelt bad - perhaps overpowered by the constant diet of tuna, soy sauce, and the fact that our only chill out area was behind two toilets... Unless you are taking your shoes off, I think its unlikely anyone will notice.
Don't feel embarrased, keep in mind the number of pax in your cabin who are farting, burping, have not washed since 1983, who over-indulged in the egg/omlette on their inbound long haul flight, bought sushi in the terminal, change their nappy on their tray table, throw up, crap their pants, have yet to wash their only pair of socks they took on their year long backpacker tour, have a fungal rash in their pants, and whom are yet to discover the miracle of soap, are sitting in your cabin.
Plenty of other smells on a 737-800!!!!