Hi Hacamila,
It's good to hear that your upper denture is working out well so far. I've had a full upper & partial lower denture for just under a year and while I don't have first hand experience with a full lower denture I know people who do.
Your mention of a bone graft suggests to me that you have some significant bone loss but that shouldn't seriously affect keeping the denture in place if you don't mind using adhesive. I've read of people who had to cut out the palate of an upper denture (so it's just a horseshoe shape like the lower) because of gagging problems and keep them in all day with a single application of adhesive. If an upper denture like that will stay in with adhesive (paste not powder) then a lower denture will stay in place too. There's also a chance you may not need adhesive. It may stay in place well enough on its own. Where appearance is concerned, you can make your whole mouth look more natural by choosing a tooth color, shade and shape to match your upper denture.
If your lower teeth are in bad shape and the implant supported denture isn't possible in the forseeable future, a full lower denture would be a good choice. If you're happy with the uppers you'll probably be happy with the lowers too. Good luck!
Yos