if you only have a shower then, install an aerated shower head as this can cut water consumption by nearly a third. You should combine this with a Combi boiler because it only heats the water that you use. There is no hot water storage tank. Don’t know what it is, find out here: What is a Combi Boiler?
All these questions often add up to one simple fact: that after you’ve bought your house, you are seriously low on money for a long time afterwards.
Maybe you can even find ex-display replacement doors if you bought a “fixer-upper” see here: uPVC Patio Doors | Sliding Patio Doors
New homes are usually very energy efficient. Extended use of insulation in the walls, roof, doors & windows mean that you consume less energy, benefit from lowered utility bills and are more environmentally friendly.
If your home is not already double glazed or you feel you need an upgrade, read this article; Your Questions answered: Our Ultimate Guide to Double Glazing UK