Being a fellow Clydesdale, I agree with jefnvk. Start with a rigid, high quality steel 90’s mtb. They are exceptionally rugged and have strong 36-hole, 26 inch wheels. Slap on some 26x1.95 smooth tires on it and ride it like crazy.
These mtb’s are exceptionally affordable used and will outlast you and me combined.
Just my two cents.