Have old Direct hot water cylinder 900 450, as you look at it in the airing cuboard there are two connections blanked off on the left hand side, these are from the old coal fire back boilers downstairs. There is one connection on the bottom right handside of cylinder, and one connection on top of the cylinder, which also has an overflow from the same to the storage tank in the loft. 3kw Immersion heater. This is my only source of hot water, and tank is in need of replacing.

Given that I no longer have the old coal fire back boilers connected. have I got to replace it with the same Direct cylinder. I ask as I have been told I could use an indirect one. Could someone please advise me on this please.
I have always carried out any (water) related plumbing that just involved pipe cutting and compression fittings myself. Many thanks in advance.