Shower pressure?

Hi, currently I am not getting enough hot water when I shower and the valve is stuck behind the tiles which I have been told is the issue. I’m basically now looking to redo the whole bathroom, however I don’t want to be in same position again with the water. I have read a lot about good showers but also hear you all saying that the shower is only as good as the water pressure from the boiler. I have a combi boiler. So if the pressure is not that great or struggling to get the hot water to the bathroom do I need to change my boiler? Your advice would be really helpful. I don’t want anymore cold showers!!!