To put winter temperature into perspective, 'Stella do Oro' does fine here where the winters go down to -30 degrees C (-22 degrees F) and sometimes below, often with very little insulating snow cover.
There are all sorts of plastic baskets that could be used to protect the seedlings from animals outdoors, and also make it easy to carry them indoors and out if the weather forecast is bad - here's a selection from Google for some ideas:
https://www.google.ca/search?q...
There are also laundry baskets and various other possibilities. If you think the cat/s will try and get in the basket with the plants if the open side is up, then while the plants are small invert the basket over them instead, or else put a second basket, sheet of plastic, bird netting, the hardware cloth that CaliFlowers suggested or something similar over the top.
A cold frame is certainly an option also but would be more expensive if you buy it instead of making it or converting something else and you'd have to be careful that the interior doesn't get too hot in the sun.
CaliFlowers, I think the change in Miracle Gro was fairly recent (past couple of years or so) but 24-8-16 now seems to be the standard analysis for All Purpose:
https://www.amazon.com/dp/B000P6QYJK/
Like you I used to prefer the tomato one before.
Edited to add picture of plants "parked" in a milk crate to keep them safe from munching wildlife:
