You are right about suspecting an Elm (genus Ulmus) from you online searches. The leaves definitely resemble an Elm species. The large "knot" in the trunk with different bark above and below suggests that your tree is a grafted specimen as well.
I searched for "Elm" and "Grafted" and came up with one example: Ulmus glabra 'Camperdownii' which is a grafted "weeping" cultivar, so Elm trees can be grafted as such. Although I am not sure about the species involved in the tree you have, it does seem similar. I will leave a couple of links below that may lead you further in the right direction.
Your additional photos show early flower buds, and they do appear to be very similar to those of "Wych Elm" (Ulmus glabra) and also "English Elm" "Ulmus procera" (a synonym of Ulmus minor - a very "polymorphic" European elm). I have attached two additional links showing the flower buds, leaves, and seeds that may help you to further confirm your tree's identity.