I have the same one from the same place. My bands are 10" x 7/8" max so I can't imagine ever needing a bigger mat.My green mat is 6" x 18" and works fine. It came with a Fiskars rotary cutter. WalMart. I have a larger mat that I haven't even used yet.
You know..... I actually had that set in my shopping cart before I decided to ask you all the question.I got this set back in 2013. Its actually cheaper now. Go figure. https://www.amazon.com/Fiskars-95237097J-Rotary-Sewing-Cutting/dp/B000B7K9UI/ref=sr_1_4?crid=199E62D8MZ000&keywords=cutting+mat+and+rotary+cutter+set&qid=1576179644&sprefix=cutting+mat%2Caps%2C219&sr=8-4
Comes with a large transparent ruler and a 45mm roller cutter. It's bigger than I usually need but no complaints. I recommend not using a metal ruler as you will get more life out of your blade from my experience.
If I was to buy again I might consider these as a set. A larger mat has been nice though when measuring out the odd looped tube set.
https://www.amazon.com/Rotary-Cutter-Self-Healing-9x12/dp/B079347RFX/ref=sr_1_18?keywords=rotary+cutter&qid=1576181684&sr=8-18
https://www.amazon.com/gp/product/B005NAGB2S/ref=ox_sc_act_title_1?smid=ATVPDKIKX0DER&psc=1#