Yes I read that. I have always questioned it myself as I have heard you should have a similar style too. But I find you can reach a wider interest if you do a bit more variety, and yes I would get bored too. I sell my work on Redbubble. I really like it as you can upload your art to different products and they print and post them internationally. I work full time and have other commitments so I don't tend to get much time to sell face to face or do illustrations on request. So it suits me. You don't make a lot of money on each sale but it does mount up and I just put it towards a weekend away. It is lovely to get a sale too. Especially knowing that people around the world have bought your art and are wearing it on a t-shirt etc. I have posted a link to my website at the top where you can find my Redbubble link. You could have a look and see if it is something you'd like to do. They do wall art and jigsaws that would be idea for your artwork. There are over 90 products to choose from