Haha, Nana to Asok terminal is like a 5 minute walk. Not really a change of pace, but I get what you're implying. If you're going mid-tier, you're probably better of in the Nana area tbh. Near Cowboy there aren't a ton of higher quality mid-tiers that are recommendable. There are a few down Soi 10, and Soi 12, but you'll have to walk the length of the Sois (seems like you want to avoid walking much).
S15 Is smack in the middle of the two BTS stations, and a decent place to stay.