A home office gives you the space you need but should this be an office in the garden or an extension that provides an office in your home.
The recent crisis with Covid 19 has seen many people working from home and a large number of businesses, along with individuals are looking to continue with home working. Where more space is needed there are various options.
In most cases the cheapest is to build a home office in the garden, kept to the right size and height this falls within permitted development and won't need planning permission.
The downsize is that the cheaper versions are high maintenance if you want to stop the investment rotting. Many will not have sufficient insulation to be a realistic option in the cold winter months.
Higher quality structures are available at £18 - £20k mark but then you have to be serious about the investment, an extension to your home, whether a loft conversion or single story extension provides a better option, it will cost more but there would be a return on that if you should sell you house in the future.