Finding something as small as the TLA-200 with an Auto setting will be difficult.
I have mostly used Braun 370 potato-mashers and Metz 40 or 45 flashes with FM2 and FE2 cameras as they can provide so much light as well as just a little fill light. The Metz 40 is a Metz 45 head with 4 AA batteries inside and very compact for its power.
A nice flash that can do double duty for your FM2n and your D750 is an SB-800. It has the advantage over an SB-900 or SB-910 if you get an FE2 or an AF-capable body of providing TTL metering as well as the Auto or i-TTL of the later models.