There are many hotels around the city center and there are many websites where you can book a hotel room. We recommend places: near Krung Thonburi Station.
Web page: https://www.hopinnhotel.com/our-hotels/hop-inn-bangkok-krung-thonburi-station
Web page: https://aimhousehotel.com
You can also follow the below steps find other hotels that would suit you better.
- go to Google search
- type "hotels at Bangkok"
- ype in the necessary information (dates, budgets, etc)
- browse through the result and find your hotel !