Here is an example of an extension tube. But do test your scope first before considering buying it. It basically adds length to the focuser so that you can reach focus with eyepieces, since moving the mirror up will push the focal point further out

https://www.amazon.com/Orion-5123-1-25-Inch-Telescope-Extension/dp/B0000XMUH8

I would not buy any filters right away if I were you because i'm not sure if they will be of any help for imaging considering you'll only be doing 30s exposures and they all tend to cut off light.