Lamina Eco AF™ 30F/-1C

I have two Mountain Hardwear bags, a Bishop Pass women's +15 and a Lamina Eco +30. I'm male, but I'm short and run cold, so the women's bag is a great winter option for for me (comfort rated at +15F (-9C), limit about +3F (-16C)). The down of the Bishop Pass still allows it to compress decently for backpacking, and it lofts up well. The Lamina is +35F (+2C)/+25F (-4C) comfort/limit, and I find it comfortable for me down to the mid-40s F (7C). It packs down quite small, and I used it for a week-long backpacking trip at Philmont in New Mexico this summer. In your situation, I'd consider two bags: the Bishop Pass 0 for winter, and a lighter-weight summer bag (since it sounds like you may not already have a good one). The credit would probably cover most if not all of the cost, and you'd be comfortable in every season.

If you're not into making your own synthetic quilt as suggested above, some sleeping bags come in both a right hand zipper and a left hand zipper and can be joined together at the zippers. Looking now I'm seeing fewer options that do this than before. ☹️ For example the Women's and Men's Mountain Hardwear Bishop Pass bags are left and right zipper respectively, but neither the Kelty Cosmic Down 20 nor the REI Magma bags seem to come in alternating zipper sides. Mountain Hardwear Lamina Eco AF comes in both left and right zips. It's a synthetic bag so it's cheaper but will be a bit heavier and take up more space in your pack than a down bag. But so would a MYOG quilt as described elsewhere.

I use a Mountain Hardwear Lamina Spark bag for this weather when sleeping without a tent. These are relatively light and not too expensive.

I think you have a valid concern. The problem is not the danger of dunking your bag in a creek, or getting it rained on, it is night after night of absorbing the moisture evaporating from your body, when there is no opportunity to dry it out. I had this happen to me in Oregon, my down bag completely collapsed and it made for a cold night. After that I bought a Lamina, which is fine but it's not as warm and heavier. If I were buying today, I would probably get a down bag with the Nikwax treated down, which supposedly is moisture resistant. I recently bought a Rab parka treated that way, but haven't really used it in wet conditions yet.