Best place to start:
https://forum.mattressunderground.com/t/how-to-look-for-and-find-the-best-mattress-for-you-read-first
Should answer alot of your questions and get you started on getting your new bed 
The link should help answer that question in more detail but generally no it doesn’t mean that it will be uncomfortable, in fact lower density foams can actually feel softer since they have more air in them, but they will not last as long as more dense foams for the most part.