Good for you, you can't beat a mongrel - as everyone has said, best place is a rescue centre or wait a couple of months till the spring / early summer and then put word round, most bitches have a spring season and there's often lots of pups (pedigree and crossbreed) needing homes then.
Do consider a Staffy or a Staffy-cross - rescue homes are full of them because they have had such a bad press due to irresponsible owners, but in the hands of a responsible owner who is prepared to put in the time for training, Staffies are great dogs - very affectionate, loyal and intelligent, and not too big so fit nicely in a overcab bunk space. They do need firm handling, and to be socialised with other dogs at an early age to prevent problems due to their fighting instincts but the reward is well worth the effort.
My Rigg the pig is a Staffy-cross (google "Rigg the pig" and go to the "About the author" page for more info) and he is my third dog - the other 2 were pure bred border collies (working sheepdogs from farms) and although I feel a bit disloyal to them saying this, he has been the easiest of the 3 to train and I can honestly say I trust him 99% with kids and other dogs (no dog is 100% reliable with kids and other dogs) whereas the collies would sometimes nip if aggravated by small children pulling their tail / ears etc and were sometimes too independent and head strong. I think he has the best of all the breeds in his genes - the collie brain, the labrador temparent and hunting instinct (very useful for fetching firewood and retrieving lost keys and gloves on the fells) and the Staffy brawn (he has a husky harness for hauling firewood on a sledge) and affectionate and loyal temperament.
Rigg is nearly 9 and still behaves like a teenager, no sign of deafness, arthritis, hip problems etc which start becoming apparent at this age in pedigrees. Apart from kennel cough, there's been no illnesses. A dog in a million.
Happy dog hunting - I hope you are strong enough to resist all those pleading eyes in the rescue homes until you find just the right dog for you. But I've always found that my dogs have found me, at times when I wasn't looking for another dog, they just kind of came along.