What Dahon adjustable handlebar stem would suit my Dahon MU XL Sport Bike

I own Dahon Mu xL Sport foldable bike and use it for exercise. I have a back problem and would like to fit a Dahon adjustable stem to keep my riding position more upright. I have tried adjusting the saddle height but am still sore after cycling.

Can you let me know, please:

• what Dahon stem would suit

• what is the likely cost

• I’m living in Ireland and finding it heard to locate a stockist. Can you suggest any store.