How old and what conditions the boiler in
Might be the time to look at alternatives if it’s coming to need doing soon.
Our boiler isn’t so We did our tank last year to replace a tired single skin 1200 titan. -we had it for 10 years….it was starting to sag out and discolour so playing with borrowed time
Had a diamond 1400 bunded from fuel tank shop fitted.
At the time came with a free outlet and Apollo watchman which is vastly better than watching the old sightglass.
My advice would be look at the shape and site of your tank carefully. We worked out that we could get a narrow thin tank and take up my less of the footprint of the old tank while increasing our capacity and it’s conciderably less intrusive into our garden