If the pod works go for it. I suspect it will turn into a PITA and not fit. In that case I would be really tempted to lay in in the hammock with the underinflated pad on top. Unzip the mummy bag and use it like a top quilt. My reasoning is that there are two issues with bottom insulation. Compression under your bottom and shoulders and cold sidewalls. The cheap bag will be less compressible combined with the pad that will probably be enough. Tucking the unzipped or partially zipped mummy over you will fill in the sides where the bottom bag does not and give you options to pull your head in a bit.
Do not forget a hat!
Be careful about over dressing. Cotton will form a damp cold layer. To much clothing bunches up and creates it's own problems. I'd start with the heaviest knit long underwear you have around and then maybe a layer of polartec fleece. No cotton. If that does not do it do not contemplate winter camping. ;-) One other trick is to use a fleece jacket loose to either form a hood or cover up an arm if you find the top quilt confining. Some of us like to burrow in, some do not. YMMV. With what you have you will survive. Comfort is something we learn with practice. Just read the threads on getting bottom quilts and pads adjusted. ;-)