Lived aboard a winter on my Alberg 30. At first it was my girlfriend at the time and I sharing one settee with a bit of old memory foam.
V-berth was sealed off with clear plastic as I was busy fixing it up. Sure took a while to get used to it!
P9000 on the bulkhead(propane). Burns external air, did OK warming the boat up.
For propane storage, I got a stainless steel fender holder from west marine(cost me about 50$ I think?) and attached it to the aft rail over the water.
Tank in there with a nylon cam strap(not the ratcheting ones). Much easier than hose clamping it to the rail or other goofy solutions, and if you're filling up every week or two you'll appreciate that.
There is an almost unlimited supply of free nylon cam straps in any town, PM me for the info on that.
Propane hose is cheap from a good industrial supplier, about 25% of the cost of poorer quality hose from a marine place. The same for a better quality regulator etc.
Once the V-berth was accessible without a tyvek suit via the hatch, I put up a heavy thermal curtain on a rod sized long enough to go 6" past the edge of the bulkead to let it get pushed completely into the head.
That hung all the way to the floor, it made a huge difference, at the worst cold we lived in salon exclusively. Think it cost me 25$ on sale at home Depot.
The single best cost to benefit was the cheap interlocking foam tiles from Home Depot again. Cut to width, trimmed the ends.
Within 20 minutes of putting them down we felt the difference in the air temperatures at leg level especially, and no more cold feet.
Easy to lift one for access to the bilge or all for cleaning the floor every few months. No worries about damage the floor with dirty boots either.
I cut another piece to fit in the v-berth hatch to insulate that too.
Memory foam feels much warmer faster when you get into bed. a Queen mattress topper would do 2 settees, or one V-berth for my boat.
Hypervent under every bedding helped for most of the year, when it got really bad I got some of the thin plastic painters use for masking, and wrapped the foam, loosely taping the open edges, in the V-berth I made sure these were in the center. Barely noticeable, but stopped the foam absorbing moisture and going moldy.
There's a cheaper version of Hypervent sold at hardware stores but it's not as nice.
I used it cut to fit in cockpit lockers too, it let water drain by without constantly soaking my stuff.
Hypervent or insulation against the hull kept clothing and belongings from molding as well.
Insulation foam, the best price to R value rating I found was Volara foam sold by the foot, it's almost identical to the blue foam(Ensolite) pads that used to be sold for sleeping on when camping. Closed cell, so no moisture issues. Armaflex was much more expensive and didn't come by the foot.
Cut and fit to the hull easily, for templating I use strips of doorskin ripped into 2" widths and glued with hot glue.
Reflectix is better than nothing but not by much, we don't make much radiant heat, so it's really got a much lower R value than suggested.
Volara is much less ugly too, and fairly durable.
For clothes and bedding storage I tried those vacuum bags and hated them, they eventually always leaked and the ziplock closure failed or got hard to manage in the cold. I went back to dry bags, I like the ones with a purge valve, pack your stuff in, close the roll top and squish the air out. Non purge ones with a bit of air left and a nice cloth cover make a good armrest on the settee.
For killing mold I tried the mold sprays(Moldex etc), they didn't do much. I preferred Pinesol with a bit of bleach instead of just bleach.
I like the smell of tea tree oil and it did kill mold in bedding, but never got it to stay emulsified in water well.
One bottle of tea tree oil added to a spray bottle of 99% rubbing alcohol, makes a great spray.
Also without the tea tree oil it's very good for cleaning electronics if they have gotten wet.