Japanese Luxman Integrated Amps

I moved 4 times between Europe and the US with hi-fi gear and used basic (but not cheapest junk) converters without any problem for decades.

Exactly, as grizzly said: basic, just not cheap junk. 

I went with a small lightweight one at the end of a cord. It has zero hum, fits easily anywhere, i.e. right behind my turntable. I plug my 100v turntable into it, and plug it into the wall outlet several feet away.

My biggest concern is forgetting the TT is 100 v and forgetting the transformer, which is why mine is just behind the TT where I can see/be reminded of it.

IF you think, I'm gonna get a bigger one just to be sure, then think about it's weight and location, the bigger the more unnecessary heat, and ...

i don't know, is there more hum potential of larger ones?

Yes! You can convert the voltage,but in high demand,it will affect the quality of sound. I do not suggest.

Go and buy the right voltage amplifier.