I think most people look smart in nice trousers and blouses/tunics with a heel if you wear them or flats if not.
All that you need to do is to make it age appropriate and you'll have an outfit that is smart but easy to wear.
I do contract work and not all though the year so don't want to invest in a work wardrobe as such. This was my staple uniform as it means I can wear them out of work too and I have always felt comfortable.
Pair each of brown and black trousers would be my starting point. If all the blouses are short sleeves what about finding a couple of mid arm length cardigans?
As for where-have you tried Matalan, M&Co, Peacocks or other cheaper places as at least then you can try and see if it's appropriate/comfy etc and not break the bank. You have said size or height!!

Hope this helps.