My brake pedal goes to the floor, it will stop you but not very well

Well I am taking a shot in the dark here, but you might just have some air in the lines. Try bleeding the brake system. Here is a how-to guide if you are up to it: https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

If you are not up to it, then it should not be terribly expensive to get it done. But just about anyone can do it.

Criss cross is not the way to do it. You are supposed to start with the right (passenger side) rear, then left (driver's side) rear, then right front, and then the left front. There is a pretty good chance that is why you still have a soft pedal. Please read the guide posted above and re-bleed the brakes. See how it feels after that and we will go from there.

They are talking about the ABS module, a common problem. But a bad ABS module will not cause a soft pedal. It will just cause you to not have ABS, so you would be driving on 1980's brakes (brakes that can be completely locked when you slam on the brakes and skid). And often times, you can get those fault codes concerning the ABS module if the grounds are loose or dirty. Plus, your ABS light and brake light would both be coming on.

When you replaced the master cylinder, did you bench bleed it before installing it? Because you could have air trapped in the master cylinder itself. If you did not bleed it, you will need to remove it, and bleed it, and then reinstall it, and very thoroughly bleed the brakes at each wheel.