3 month old too heavy for PnP bassinet...Don't want to put him on floor position yet for nighttime nursing. DIY options possible?

TLDR: wanting safe, small-bedroom-friendly option for LO to sleep in next to the bed that is closer to the size of a crib and elevated for easy nighttime access.

In my search for thin PnP mattress toppers for the highest position/bassinet feature for my 3 month old, I was shocked to realize that you're only supposed to use it up until 15 lbs (in the craziness that has been my life these past 12 weeks, I haven't had a chance to read the instructions for the PnP...bad mommy), and little guy is now definitely over 15 lbs.

I love the convenience of having him that high next to me in bed for nighttime feedings and diaper changes and am not ready for him to sleep on the lowest setting which is basically on the floor. He has a normal-sized crib in his own bedroom but I'm most definitely not ready for that yet and the crib is way too big to put in our BR (plus we'd have to disassemble/reassemble it which I think my husband would rather gouge out his left eye than have to do again). Has anyone done any DIY work to elevate the mattress on the PnP so that it's higher than the lowest setting but reinforced for safety? Like building a frame of some sort? I'd hate to go out and buy a whole new sleeping apparatus just so that I can change and feed him easily at night while keeping him used to sleeping in more open space (to prepare him for his crib in a few months...don't really want to go back so something smaller like a side car-type situation or the rock n' play). Maybe just buying a 2nd hand mini-crib is the answer? Or am I making too big a deal out of this and the bassinet is fine to use for awhile longer? Mommyanxiety FTL.