I bought a set of maps from one of those hard working guys selling printed materials as you wait at stop lights or in traffic jams around Yangon. I scanned the map set of 15 Townships of Yangon plus the full city map at 3500×4900 so you should have good detail.
I was able to find some better quality topographic maps from the British published in 1962. This set of Yangon scans will be good enough to get you to the places you need to visit. Especially if you are looking at places to rent, neighborhoods are easily recognizable.