Arm rests on the lounge unit are a possibility , my water skinks love these ( gap under them).
In the gap where the backrest and seat is on the lounge , my skinks have all squeezed in there on occasion (only found them because I spotted a tail poking out).
Inside the lounge (if the webbing on the underside of the bases is loose , they also get in there sometimes (I've taken webbing off to do repairs on my old lounge and the dragons and skinks love the cozy dark void and have climbed up inside as high as the go.
Dragons and skinks are extremely inquisitive, I warn all my visitors - not to leave open handbags or backpacks or other bags on the floor , I have currently have 3 wild water skinks and a wild velvet gecko (spotted it last night) living inside my house and visiting almost daily and they are all super inquisitive and apt to want to investigate new items on the floor (very intimately by crawling / climbing inside it) and might become accidential stowaways when the visitor/s leave....LOL , this may have happened to you little juvenile dragon , or he may be curled up in school bag, laptop bag or handbag .... worth checking or asking any visitors to check.
if you have an attached garage .... check under the wheelarches and near the exhaust pipe and around the engine .... these may have been warm enough to be attractive to him if he got into the garage. This is common hiding place for snakes and lizards (and cats) here .
I'm sure unless a door was ajar or there is enough crawl space under doors , that he's still inside.
If it's not Arctic conditions where you are (or FREEZING overnight) check where ever the sun shines onto concrete or paving in the mornings or afternoons , if he's outside , and not hiding and sleeping , he'll likely come out and basking on warmed concrete or paving when the sun's been on it for a while.
i hope he's still inside as sub 32F conditions outside will kill him .... these temperatures never occur in their natural range , only the occasional morning frost .
If there is warm place under the house , you need to consider the possibility that he's slipped through the front or back door , and may be in the she or garage or hiding in the garden under a shrub or under some ground cover flowering plants or even curled where ever your heating plant is.