yes you can buy the red jackets. I actually have two round my cylinder although it has the factory foam, as I had enough room and they are cheap to buy.
factory foam, in rising order of quality and newness: yellow, green, blue.
you are probably losing a lot of heat from the pipes, especially those between boiler and cylinder or around the pump. Measure the pipes, they are probably mostly 22mm diameter but you may have some 15mm, and in an old house, possibly some 28mm.
You can get pipe lagging like Climaflex or own-brand substitites. Have a look in DIY sheds. It is made of stiff polythene foam. It has a partially cut slit down the side so you can push it round the pipes. Use tape to prevent the slit gaping especially at bends and fittings. You can cut and trim it with a serrated steaknife or breadknife. Turn the slit to the side of bends. 28mm is hard to come by but you may get it in a larger plumbers or builders merchant.
There is a BS grade (sometimes called "Byelaw") which is as thick as your arm, and is specified for pipes in unheated areas such as outbuildings, lofts and under floors. The economy grade is not as good but is easier to fit and cheaper.
Neither is expensive.
Sometimes red jackets and pipe lagging are subsidised, but there seem to be no subsidised ones on the market this year.