Looking for a specialy made hot water bottle

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My name is Tania, i live in the uk and i am looking to have at any cost as i am desparate. A specialy made hot water bottle to cover the whole of my back. i have joint hyper mobility syndrome,spondilosysthesis grade4,fibromoralgia,arthritis, and i struggle with pain daily and i use the average hot water bottles but one for upper and one for lower back but its hard to keep the upper in place. I said to my partner, i need one big one. He responded by saying it doesnt hurt to ask, 40×20 in size is probably about right, would that be at all possible to make please. I figured it cost nothing to ask even if your unable. I appreciate the time taken out to read this request. Thankyou
Tania