After killing my last rubber plant through over watering, I've been very careful not to do the same. So much so, that I came back from holiday to find all the leaves drooping. I watered it but a month later the leaves are still falling off every day! I'm watering from the bottom so the soil at the top still feels quite dry. Is it getting enough water? What should I do!? The top leaf has never perked up since I underwatered it! When I put my finger down through the soil it doesn't feel very compact at all]1
Depending on the type of soil you used and how much water you are giving through the bottom it may not be enough. If it is very well draining soil it will have a more difficult time absorbing water beyond a certain point, even sitting in water all the time. The water has to travel up, against gravity.
The other is how much water are you giving. Do you keep giving it water until it stop absorbing water, or just give it a portion of water, like a cup.
The best thing you can do is invest in long bamboo barbecue skewers. Insert the skewer into the soil. Wait 30 mins or longer then pull it out and look at how wet the soil actually is. From that stick you will know when to water. You will also know how deep you need to make your watering tray for it to absorb water.
If it a typical peat and perlite or coir and perlite mix, you will not need that deep of tray, but you will need to wait 10-15 mins for it to absorb water, before you dump the tray out. In 5-10 mins check your skewer, it may have absorb water quite fast. If it is only absorbing water part of the way up the pot then you need to add more water, making it deeper easier to absorb. It does not need to get to the top of the soil. It just need to cover the roots. Leaving the top dry cuts down on possibility of fungus gnats. You do not want to leave it in the soil too long, then it will absorb too much water. You do not want to water log the roots of your plant.
You can stake up that leaning limb with a bamboo or covered metal stick.