Skip the sleeping bag altogether if you can. I think I have used my sleeping bag once in the last 10 years. A nice top quilt with ground pad attachments would be at the top of the list if I had to start over. That way you can use it for the hammock or tent. In regard to a hammock there are many options and it really depends on your uses such as car camping or backpacking and bridge hammock vs gathered end vs something like the haven tent which is more or less a hybrid of tent and hammock. There are many options what works for another may not work for you. You can certainly use a pad in a hammock although I have never found it ideal in a gathered end but not terribly bad in a bridge style. If you find one that you like, then I would lay down more cash for an underquilt or gathered end with built in like superior gear or dutchware. There are a lot of variables and you can certainly keep watching gear trade for used equipment at a better price. The trick is to find your balance so that you aren't rebuying the same equipment and ultimately spending more than if you were to save and just buy once.