To me it's a bit like buying a car. Spend little, spend a lot.

Newer beds tend to be higher. Something you realise when shopping for bed sheets, especially fitted ones that come in different depths. Personally, I don't like memory foam. I much prefer a conventional mattress, adding a topper.

There's nothing wrong with buying a brand new bed online. Here in the UK, they are delivered from the manufacturer either to store or direct to customer. You'd be very unlucky if you got bugs, etc from these. Measurements are included on websites so cuts the embarrassment of not fitting the room, lol! I've bought an armchair online and plan to get matching sofa. Cheaper than going into store.

I have a good quality double. Enough room, just, to get round it. Problem arises when I want to turn the mattress. Whole job takes 30 minutes. Have to close the door so ensure I have phone with me as you can guarantee someone will call in the middle of the job!!

Good luck