Buggy recommendations for small, low muscle tone baby

[Cuppachaplz]

Can anyone recommend me a buggy or pram for a baby with low muscle tone.
DS is 8 m old, but unable to sit, or hold his head. He has outgrown the newborn/pram fitting for our jogger, but the seat has very little support, doesn't recline and the harness is far too big.
I'm looking for a stroller/jogger/buggy which can recline flat, provides goor support and has a harness which adjusts small enough for my 12b baby.
Ideally, I would like a permanently fixed front wheel (or wheels) as opposed to fixable, as I run (although obviously not with baby at present). I appreciate this is unlikely, but if I'm asking for my dream buggy...
It needs to be OK off road too due to where we live.
Thanks in advance

Dc1 didn't sit up until 11 months so I've been there myself, I found the silver cross pop was fantastic as it doesn't have set positions, you pull a toggle thing at the back and recline it as much as needed, it's up to 25kg as well which fits the bigger kids in

It has a good suspension and the wheels are durable, I've been all over the place with mine and it's still in good knick

That might be something to look at?