The smallest you can get with the current tech is one foot two or so.
With ST penalty of eight, and a IQ penalty of two.
And it would need twelve meals a day, and a warm environment.
“She'd become a governess. It was one of the few jobs a known lady could do. And she'd taken to it well. She'd sworn that if she did indeed ever find herself dancing on rooftops with chimney sweeps she'd beat herself to death with her own umbrella.”
― Hogfather