Hi 808
Lots of boards, so long answer.
It sounds like you are possibly going to flat-water paddle more than surf, if that is the case, you should gear more towards a good paddler, that also surf well.
Your 10 Mana is a great board for both.
I loved paddling and surfing my 10' Mana, so I know it well.
My suggestions for you are:
10' Steeze
9'7 Creek
Explanations below
9'6 Flow - has a lot of rail curve, has quite a lot of yaw, so not the ideal flat-water paddler... easy surfer for intermediate. Super Stable
9'5 Speeed - nose pushes a bit of water when paddling flat-water, but paddles straight. the 9'5 may be a good solution since it is stable, surfs well. The longer the Speeed, the more you have to move around on the board to turn.
9'2 Skate- great paddler, stable, surfs awesome.... but is best in low power waves with flatter faces. Steep waves are difficult because of low nose kick.
Shroom- A quiver board that is super fun, but in a narrow range of wave conditions. Under 4' and soft are best.
The sizes you mention are HUGE.... the 8'7 was really big for me at 108 kg
If you want to keep a similar type of board to your Mana, I would go with the 10' Steeze.
It will be lighter, snappier and more durable, so a very nice upgrade IMO
Reason for 10' Steeze over the 9'6:
I paddled my 9'6 quite a lot in Florida, but as you saw in my review of the 9'6,
I was surprised when it wasn't the floaty big board I was expecting....
and a bit tippier than you might be looking for in surf, so the extra length and volume of the 10'er might be appreciated.
The Steeze is a low rocker board with straightish rails, so it moves well when paddling and easy speed on low power waves.
As you saw in the video, I feel a center fin over 5.75" made it sticky for me... but others like the bigger fins.
The Steeze is definitely a "longboard" style ride, especially at the 10' size
A good choice that I think you will be very happy with if you want to stay with the "longboard" feel
If you really want easy stability and easy performance, with very good paddling characteristics,
I'd suggest:
the 9'7 x 33" Creek at 160 liters.
Super stable and will handle any surf conditions.... and is very easy to surf in a more "shortboard" style
My 9'4 Creek is noticeably more stable than my 9'6 Steeze.... and others who I have swapped back and forth with feel the same.
The 9'7 at 33" will be rock solid
One thing I have found with the Creek, is that in low power waves, a bigger Creek works better, and will still rip in good surf.
Smaller Creeks are super high performing contest winners, at the Pro level.....
9'7 x 33" Creek is fine for most
anyone under 115 kg
Go see John, Guy or Mike at SurfFX and demo the biggest Creek they have, to get a feel for stability, paddle-ability and overall feel.
Tell them Creek sent you

PS
As SunnyBuoy suggested, the 9'5 Soul is also worth considering... some are still available at dealers around OZ
and I am sure you can order one from Surf FX
It is a good paddler, pretty good stability and surfs really well.
Here's a vid of me surfing the 9'5 SOUL last week... with biggish sidebites (5.25") and a very small center fin (3.5")
I chose it that day because I wanted a board to connect the outside with the inside, but still be more shortboard style surfing.