If your thoughts are turning to putting away the diving gear until Spring then I invite you to reconsider that decision and research drysuit diving to extend your diving year. A quality drysuit (I own several and select depending upon the environment) will last for years- see blog below and you will quickly realise value for money.
A drysuit is not the end however. Insulation is key and a high quality loft undergarment, layered, will be just the ticket. Weezle make excellent undergarments, Diving Concepts and DUI too- there are many others out there also. But you do not have to purchase dive specific insulation- other sport quality layers can be multifunctional too. My base layers for diving and cold weather adventure racing are Patagonia base layers, built on that might be a Berghaus fleece and I am toasty in all but the coldest of waters- and for those I pull out the heavier Patagonia fleeces. Restriction of movement is something to be wary of.
On my head, I might add a thin beanie under my hood and either wetgloves with or without a liner or dry gloves for extremely cold conditions.
Watch for the toes, too. Quality, warm socks such as those used by hunters ones are first class.
Argon inflation is not necessary, although it is pleasant if you have it.
Get some advice from your local quality dive store re suits, fitting, undergarments (many suits come with undergarments as a package deal) and seek out a quality instructor who regularly dives a drysuit and who accordingly will advance you in dry suit diving skills and train right! There is much, much more to drysuit than is covered in a specialty programme.
Be safe. Train Right!