I have to remove two conifers on either side of my chimney this fall and would like to replace them with a pair of Japanese Maples. I am located in the foothills of the Cascade mountains northeast of Seattle. The chimney is on a south facing wall and gets full sun for about 12 hours in summer. Winters are relatively mild with rare occasions when temperatures will drop below 20 F. The proper tree should be narrow, maximum width of about 4' and height up to 12-18'. I am quite capable of pruning to maintain shape but don't want to have to do that at height over about 9'. Any and all suggestions would be greatly appreciated.