How far from extension for a sunken trampoline? And size of trampoline.

[LadyCurd]

We have a tiny pointless quarter circle of grass in our small garden about 11ft by 11ft. We never mow it (we mean too but not gardeners!) or use it so think it might be better served by putting a sunken trampoline in the space. Sunken means we won't bother with a net (wil prob have gym mats and soft bark) as that would block most of light into bathroom window (downstairs extension), also means we can open shed doors fully as a standard trampoline would hinder this.
Thinking an 8ft trampoline would probably fit best in the space as 10ft prob too close to extension. Do they even do 9ft ones!? But is an 8ft one worth it size wise (we have two kids and a third on way), I see the bigger ones getting so much more use than the smaller ones, and obviously sunken trampolines being so so much more expensive to install then we need to make sure is worth it. Also worried about risks to foundations of extension is a 2-3ft clearance to dig to sink a trampoline sufficient or still a bit risky?
Is this idea a non-starter!?

We have a sunken one - it's a massive 16foot one in a far corner of the garden - I've noticed kids get a bit over excited on it and therefore in quite pleased that it's away from walls, fences and the house ! They often jump on and off and you'd be surprised how far away from it they land !! so be careful putting it close to hard surfaces /edges of walls fences etc !
Ours has pea gravel back fill going to about 2ft back around it all - the hole was massive - but I was assured it was needed for drainage and to hold back the earth etc been in about 10 years now - and still used every week ! ( not by me though unless very tipsy !)
Personally I think the bigger ones have move give and are less dangerous than the smaller ones - which seem to be tighter and ping kids around and often off more often.