Question: I am planning to purchase a travel router or VPN for my upcoming trip to Thailand. Which one is better?

Hello, I will spend the next few years without interruption in Thailand and I have a question regarding Internet. I am planning to buy a sim card with unlimited traffic, it will cost about 900THB per month. I would like to know if it is possible to get a second sim card for the same number so I can use it as a wifi source for my apartment. For example I can use an old phone and activate the Mobile Hotspot. Alternatively there are routers that can be equipped with a sim card. So I would always have wifi at home and also on the road unlimited internet. Can anyone tell me if this is possible?

Edit: When i say unlimited, i mean no speed limitations after a certain amount of monthly usage.