IMo first find a proper home for the TV thta is way too high for proper viewing . As for the FP redo I find it easiest to just draw the FP to scale and add different size tiles easily in a drawing so I copy the initail drawing then on each copy I drw different tile sizes showing grout lines and then use those to color in different color tile .. Is this a wood burning FP ? Where I lve you do not need a hearth for a gas FP so you need to know that and if you really want any help here we need to know the whole floor plan to scale and your style .

I've been creating mockups for about 30 years, so it comes pretty easy for me...but I'm not aware of any particular software that does not have a pretty high learning curve.

Maybe I can help you. Do you have an idea what you would like to see?

Here's an example of a steel mantel surround that will help protect your TV from excess heat.