Acclimating to cold water swims

Hi folk, My goal may be a bit grandiose, but my aim in two years is to do the Boston Light Swim. I'm no star, no speedster, but I did complete the 5.4 mile swim about which I posted a few weeks ago. I'm not sure the water temp for that swim, but just my guess is that it was somewhere in the 70s, maybe high seventies? I didn't wear a wetsuit and never felt the need for one, although I was beginning to feel mildly chilly in the last half mile--nothing really significant. It wasn't to the point of real discomfort, and I wrote it off as a bit of fatigue--but as I was going to finish soon, it didn't bother me all that much. I think next year may be too soon to aim for it, since I have a few things in mind that I need to accomplish before I take it on: 1. Improve speed--I did that to some extent to make the 4 hour cut-off for this year's swim, but I'd need to improve more to go under 5 hours for 8 miles. 2. Adapt to cold water. I will say I often have enjoyed cold water--during a hiking trip in NH, there was a swim break in a pond that was quite cold (not sure of temp but everyone gasped when the got in), and I was the only adult female to swim; during an Outward Bound course in Maine, the one thing I most enjoyed doing was taking that jump off the 12 foot pier into Penobscot Bay in late May. In a mile ocean swim I did several years ago, the organizers recommended wetsuits b/c the temp would be in the 60s. I didn't wear one and had no problems w/ the water temp (the breakers, now that was another issue--but water temp was fine). Still, I've become a bit too used to warmer water lately so need to find my way back to some more cold tolerance. Finally, 3. Need to save those pennies--I see it's a more expensive swim than those I've done! (My focus is on no. 2, but feel free if you have any suggestions for no. 3 to toss them into the thread.) Okay, so experienced cold water swimmers, your tips? One thing I plan to do during the fall season: I belong to an open water swim group, and we do a river swim once a week (distance is flexible--people do what they feel ready for). I understand this swim could keep being held through October. So I see that as an opportunity to acclimate. I'm thinking of a longish swim next year in a colder environment--I want to still do the same one I did this year only improve the speed, but thinking to add another long one. Do you necessarily have to gain much weight to deal with cold water swims? I also run so I don't want to gain if possible, but maybe it's a survival thing too. I'm also posting here b/c if I put my plan on the internet, I'm less likely to back down and think, "Am I crazy? That's too long!" (Both true, btw, but that's what I thought of the 5 miler and still did it three times.) So this is my way of committing to the plan--or some might say I should be committed, but no comment there! ;)