Investing in a high-end monitor, even if you are running a laptop, will result in much higher productivity and will make your home office feel more established.
A larger display allows users to view more of a document or a web page at one time, facilitating faster-paced work. Larger, high-resolution monitors are also much easier on the eyes. Try working from a laptop screen for a month, then you will understand the importance of a good, large monitor.

These days monitors need not take up much space, and are almost always flat-screen and lightweight so you should still be able to structure your home office design around them quite easily.