You can also purchase an adjustable threshold, if it would help.
Compression style weather stripping, sized to fit the air gap will markedly cut down on air infiltration. It also comes in a foam style that self asheres to your door frame, which you clean well with alcohol, prior to application.
Take a trip to Home Depot and check these out in the weatherstripping section. The staff are pretty helpful. Take a few pictures of your door with you, so staff can show you how to adhere the self stck type, or whatever is best.
The packages are pretty self explanatory, and further guidance can be found on You Tube videos. I know you can do this!
Look around on the internet for tips on installation and products. I have found the This Old House and the Family Handyman websites both have a lot of fix-it information.
One other thing: I've found those draft stoppers to be really helpful. They are the long cloth tubes, filled with some sort of sandy substance, that you place right up against the bottom of the door. They're cheap and easy to use. They've made a room in our house that has two outside doors much more comfortable!
Door weather stripping kit and a door sweep on the bottom of the door.
https://www.familyhandyman.com/doors/door-weather-stripping/view-all/
Rubber strips.
You can also purchase an adjustable threshold, if it would help.
Compression style weather stripping, sized to fit the air gap will markedly cut down on air infiltration. It also comes in a foam style that self asheres to your door frame, which you clean well with alcohol, prior to application.
also caulk around the door frame and around knobs and locks.
Look around on the internet for tips on installation and products. I have found the This Old House and the Family Handyman websites both have a lot of fix-it information.
You can also use duck tape until you get what you want. Sounds weird but it works