There is another techniqiue which was common when cameras only went to 1000 ISO.
It is based on the point that irrespective of anything else the important thing is to have sharp photos. Unsharp images cannot be corrected while poor colour can usually be fixed, along with noise, in editing.
SO the technique is to pick the suitable shutter speed and then in editing raise the dark photos in editing using NOT the brightness/contrast tool but either Levels or Curves which permit you to raise dark tones without blowing highlights that the simple B/C tool will normally do.
As a newbie you probably are not that familiar with an editing programme, maybe you do not even have one, so rather than investing in equipment which will rarely be used it is better to get a good editing programme such as [at least] Elements or better Paint Shop Pro [ which will not break the bank ] or Photoshop Cloud which unfortunately commits you to a regular payment whether you use it or not. If you want to try flash I suggest that you let the camera do it for you ... I have numerous flash units which rarely get used becuase I find that when I need extra light the built-in flash is quite adequate and should not be dismissed as so often one reads in photo circles.
I have not used this technique for some time now because with the advances in cameras I know that I can safely work at 6400 ISO for family shots which do not require anything bigger than a monitor screen size. But a one or two stop under exposure is perfectly valid with a good camera .... bridge, MFT, or APS-C. The only drawback is that you need to have confidence in what you are shooting as it is unlikely you will be able to view the results in-camera and have to wait until they are opened in your editor. Not a problem for me as I rarely 'chimp'