The brass-cylinder pump sold for $50 by Sears Craftsman as an automotive tool is high quality. So are Mity Vac brake bleeder kits, usually about $45. I'm not sure whether either are available in the U.K., but look at them to see what a quality pump is. Get tubes that have the white acetal plastic quick-connects....that's a basic indicator that the product is intended for regular use rather than the cheap sex shop novelty pumps.
Bathmate products are popular but lack a gauge, which in my opinion is crucial to safe usage...it's very easy to underestimate how much vacuum pressure you're applying, which can lead to spotting, blisters and bruising.
You'll see a lot of advice especially from tube manufacturers to get a tube only slightly larger than your girth, to "pack" it and then move up in size. While great for tube sales this is of no real value. Your penis neither knows nor cares how much space exists between it and the tube walls. Packing the tube ceases any girth gain.
In the same vein, air versus water pumping....a vacuum is a vacuum is a vacuum...the medium is irrelevant. If warmth matters and feels better, wrap the tube with a heating pad. Water pumping...in my opinion...is a pain in the ass and can lead to messy accidents.
Pumping is great for quick effective *temporary* girth gains, and nearly useless for length gains as packing a tube to gain length will far too often lead to painful blistering of the glans and "donut effect" of the foreskin from spending too much time or using too much pressure. As regards permanent gains, everyone is different, but consistent use is the one constant requirement.
An internet search for "penis pumping" etc. will reveal the several serious manufacturers. See what's available near you and post what interests you, others and I can offer advice on what you find.
And always remember that pain means STOP.