As well as P Fruiticosa I have two other shrubby potentillas (about 20 years old so labels long gone). Leaves and flowers are the same as P Fruiticosa but the stems are more upright and woody.
What colour are the flowers? This link may help it has a list by flower colour a couple get mentioned as being upright. Maybe you can study that. eg page 6 mentions Mount Everest as upright...white flowers.
@Silver Surfer. Thanks for the link. 'Mount Everest' is a contender but I think they are probably 'Wychbold White' (last on the list) bred by Webbs of Wychbold as I bought a lot of plants from them when my daughter lived in that area.
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In the sticks near Peterborough
This link may help it has a list by flower colour a couple get mentioned as being upright.
Maybe you can study that.
eg page 6 mentions Mount Everest as upright...white flowers.
https://www.rhs.org.uk/Plants/PDFs/Plant-trials-and-awards/Plant-bulletins/Potentilla.pdf
'Mount Everest' is a contender but I think they are probably 'Wychbold White' (last on the list) bred by Webbs of Wychbold as I bought a lot of plants from them when my daughter lived in that area.