If you are unsure that the wetsuit you are looking at is going to be warm enough for you, you may want to consider linings. See, when a lining is added to a wetsuit it does wonders for the warmth as it improves the thermal properties of the wetsuit itself. This can be ideal if you are planning on diving in waters that creep under 50 degrees Fahrenheit. Plus, again, as you dive deeper the water continuously gets colder and the extra insulation may be necessary.
Past the warmth, a lining can also a very soft and comfortable feel, depending on the lining. For example, plush linings will significantly increase the feel and comfort of your dive.