I don't know whether they sell yours, but we get ours from Tesco for our HP (301 black and colour) - if you get them on special offer, they are good value.
Can't help with the ink. HP always seems most expensive for ink. Next time you replace your printer consider an Epson. The compatible ink cartridges are really cheap.
Graham-W, done that recently, and bought 4 cartridges because they were cheap, then found the printer didn't do what it said, i.e. enlarge and reduce so had to send it back. Then started thinking nothing wrong with HP printer see what we can sort out on cheaper inks.
I can't offer anything specific about HP cartridges but I get Epson compatible ones from local Cartridge World shop. No problems with them so far so might be worth a look for you if there is one near you.
I buy mine on line from http://www.justinkandpaper.com/ They are in the Channel Islands. I find them satisfactory and less expensive than some other on-line sources. Whether they would meet your needs I don't know