Another option would be to upgrade the pipe size, over time the internal diameter of the pipe decreases due to scale build up. In certain areas this may be worse than others.

Low pressure could also happen because stop taps are not opened fully.

The quickest and most simple option would be to get a booster pump but they can be noisy, different makes and models come with longer warranties than others.

Hope this information helps

first of all get in touch with your water provider to see what you can expect in the way of pressure and volume from them,increase the size of your incoming main to provide as much pressure and volume.if you get good pressure and volume of water i would go for an unvented cylinder,it may be as well to increase sizes of hot and cold service pipework as well,get a qualified plumber to work out your volume needs for each appliance and size pipework accordingly ,this will all cost money but get it right now and save yourself trouble in the future.

Check out some of the online shower pumps, and mains water booster pumps.