First, I'll tell you what I will be doing, then I'll give you my 100% applicable story of what I have done.
I live in an unusual house on 13 some odd acres of forest. The property has tons of springs and small streams that form so although that's a good amount of land, the prior owner and builder of the house did probably a dozen test perc holes that all failed. Anyways....I've looked into downsizing not only to a smaller house but to one in a cheaper nearby town. Way cheaper. I've done the math (I've got 3 engineering degrees). And what I've found is that unless I'm going into some small apartment rental, I'll save nothing, zilch, nada. So be SURE you calculate in all the costs to sell and all the costs to buy. You may be so surprised that you end up doing what I now plan. To die in my present house.
Ok...what I did. Our previous 800 square foot starter home went on the market not long before reaching agreement to purchase our present house. We included a contingency that we first needed to sell out existing house. This, of course could be a huge sticking point, but we were written specifically into the seller's realty agreement as we came to them before they contracted a real estate agent. So if we bought the house, no commission for the agent.
Anyways....how'd that work? We actually accepted an offer 3 weeks later. We lost some money on that house, but this was the end of 91 and Massachusetts housing was nose diving following a housing bubble. We set up closings for both houses for the same day. In the morning, we attended the closing with our lawyer, selling the house. In the afternoon, we joined our friends at our house to finish any last thing to load into the truck and it was off to the new house. While in transit (all of 6 miles), our lawyer handled the buying. After his closing, he met us at the new house for any last signatures and such and we were done.
I would highly recommend you hold yard sales, craigslist the crap out of all your belongings and make it so you can easily move without paying someone to help. Heck....coming up to the closing day, I was at Home Depot returning a 2x4 I had bought a year earlier. I wanted everything possible gone.