hey benno
i'm 90kg too, and when coming back from a bad knee and and leg injury, a mate organised an inflatable sup for me (through a chinese manufacturing contact, but turned out to be identical as far as i could tell, to the C4s) to ease my way back on the water and to break the rehab boredom.
started on river, and yeah, they do bend a bit, even when pumped to 12psi, but i took it out on some 4km or so adventures and it would cruise fine once you worked on your technique. got it in the ocean and waves as soon as i was confident (well, actually before i was really ready, but everything turned out fine

) and the first thing is that the flex gets magnified 10 fold with waves, that is when actually riding, but also when dealing with chop and paddling out etc - it takes some getting used to - but if you are after fun, and not performance, i'm sure you'll be right. the next thing is that with any wind, these bad boys try to swing quicker than a compass - you will need really glassy conditions to be able to relax and enjoy, otherwise it is a real battle. that follows on to making sure you get one with decent detachable fins, and a longer centre fin will definitely help (or even by itself and just ride like a mal) - don't go for the molded hard rubber fins that are already attached on some sorts.
your kids will love it though, and it is heaps safer and user friendly for those fall backwards moments when learning - my girlfriend doesn't know why i come home with all these bruises and fin chops after i surf on short boards - as she is used to the mattress as i call it haha
finally a general comment as i don't post here often, SUP is definitely small wave fun and great exercise, but i have upgraded to a new board myself and used a few major brand name boards of of friends of the less inflatable variety now, and i can honestly say despite the froth evident on these forums, that it does not even come close to shortboards for surfing performance when the waves are good (despite the skills shown by keahi and the crew at the nationals, i mean, they'd be throwing alaia's around if they spent enough time on em), so don't sweat on choosing between an inflatable or some other tank on "surfing" performance, go the convenience to match your needs... and surf when it's pumping.
hope that helps.