Phoebe, do hope your venture goes well. I am almost 70, am 5'1" (or I was!) so definitely in the undertall category. Separates are what I go for as dresses etc are always wrong in the waist for me. Pants that are designated as 7/8 on other people often work well as full length on me.
My wardrobe these days is mostly pants, skinny, with mid thigh tunic tops that cover the bumpy bits. Tunic tops can be short sleeved, three quarter or long. The fabric and accessories indicate whether casual or more formal. You can do a lot with black pants, a simple tunic top and a stunning necklace.
This wardrobe covers all seasons with fabric adjusted as needed. I like merino fine wool knits and stylish long cardigans to accommodate weather changes. I always choose plain fabrics, no patterns and dress up with interesting necklaces often purchased on my travels, earrings and scarves and pashminas. It works for me. Good luck.