What shape are you?
I'm a petite too, I don't usually wear separates as I find it difficult to find trousers or skirts in the right length so I'm not sure whether this will help 
I've got about 8 good quality blazers, loads of cardigans and dresses. I mix mid price with cheaper items.
You say Hobbs doesn't fit you are you trying their petite or regular range? I'd recommend their petite blazers. Their dresses can be lovely but I have to be choosy, generally I only buy their short or knee length dresses as midi is the wrong length on me.
Reiss can be good for dresses, also Jigsaw, L K Bennett, White Stuff, Fat Face, Hush, French Connection, Ted Baker, Anthropologie, Sezane, occasionally All Saints.
There can be good finds in Zara, Next and M&S but be picky and check the fabrics - polyester can be shiny, sweaty and uncomfortable. Boden's petite range is a good fit but beware the wacky prints.
For cheaper dresses Oasis, Warehouse, Gap, Top Shop, ASOS, very occasionally New Look.
eBay can be good for cheap finds.
Does that help OP?