Clean Republic has a nice 250w front hub that is extremely easy to install, small and unobtrusive if you want your bike to pass at first glance to look exactly like a "regular" bike, and will certainly help on the hills, but can't surmount anything other than a mild slope on its own. You will need to pedal. Finger tip throttle only. They also have a 350w kit with a variable thumb throttle. This size motor is more agressive when it comes to hills. The hub is bigger, however, and gives the donor bike more of an "ebike" look. I purchased my 250w kit with two 20 mile lithium batteries from them several years ago, and still love using it. It is my favorite bike to ride anywhere and everywhere, and no one has ever been able to discern that it is anything other than a simple vintage hybrid bike. The motor is so small that it just doesn't stand out.
They are a very reputable company with excellent customer service, and excellent products. US based, west coast.
https://www.electric-bike-kit.com/hill-topper.aspx