Aged 33 you probably don't feel the cold, but if in January you are freezing I recommend ski trousers (the cheapest you can get, probably from eBay). 12 years ago I bought a pair that comes up over the lower back, with integral braces, and when others dithered I went flying. A windproof outer layer is essential - anything from a cagoule to a proper flying suit.
Good luck with your training - I started in September and went solo in April (with no soaring in between) and by the end of the following summer had my bronze and was on my way to Silver (this is important - Silver badge makes you a real glider pilot, entitled to break club gliders without supervision). Learning in winter is really good (except for the scrubbed days. By the time I went solo I'd launched and landed in howling gales, horrendous crosswinds, rain showers, with misting canopy etc - summer flying was dead easy apart from those pesky thermals. And crisp, bright winter days are magical for flying.
In terms of books, much depends on your thinking style. I'm pretty analytical and found Piggott less use until well after solo. Ken Stewart's Glider Pilot's Handbook worked well for me. If you're more a "get the feel for it" person, then Piggott is definitely for you, and you'll find Stewart rather dry and technical.
Two pieces of advice for the beginning glider pilot:
1. Join in. Fetch cables, drive the tractor, push gliders around etc. This is more fun than standing still in the cold, and integrates you into the club workings. People will be pleased you joined, and you will be treated very well. Also you learn stuff - you'll fly a better winch launch once you know what the winch driver hates, or what drives the tug pilot mad. Someone who treats the club like a shop and moans because they're getting poor service inevitably alienates the other members, who are after all working for free to get you flying. Many times during training club members went out of their way to e.g. fetch another set of cable so I could fly again, when really everyone else except me wanted to finish for the day. Not cynical behaviour on my part, just how I took to it, but looking back I can see occasions when less motivated trainees would not get that extra bit of help.
2. Ask questions. Everyone has wonderful exploits they want to relate, or some pearl of wisdom to impart. So long as you don't believe any of them until they've been confirmed by a reputable source, you can learn a lot.
Fourteen years on I'm still fascinated, own my own glider, but still haven't managed that 500km flight.