My picture window in LR is always cold in winter n hot in summer. The windows been there since 1966.
Windows that old are undoubtedly single pane. These windows are notoriously known for being inefficient and they allow heat exchange in and out. They leak not only through the window, but around it too. This means that even if you seal the window with one of the kits you will still have very leaky windows. Without replacing your windows (which is truly the only real solution) you can install one of the kits with the Saran Wrap type stuff. Then pull off the window casing (trim). Once it’s removed you can drill small holes in the drywall and shoot expanding foam into the cavity. Make sure to go slow or the foam will expand too much and destroy your drywall.
There is a film you can put on the in side of the windows that will help keep out both you can usually purchase it at places like Home Depot or Lowes
Sounds like you need to update and replace that old window, there is too much heat/cold exchange going on. There are windows out there that will control that problem. You might consider contacting reputable window companies for free estimates, be sure they are licensed and bonded. Try Angie's List for some, Home Advisor, or a local paper.
If you are not readuy to replace the window, I could suggest thermal drapes for that window, we did just that for our patio doors. Got them from Walmart and they work great.
For the winter months, you could also put up plastic sheets designed for that purpose, available at diy stores and of course Amazon.
Best to you.
My mom's house was built in the 20's, and it is a huge window! Roughly 8' x 8'. I had to replace the window, and it cost extra as I wanted to preserve the architectural detail of the original installation. If that isn't an option at this time, Redcatcec has excellent suggestions.