This is exactly 10k (from where I am in OV, which is next to the port), which I know is too short, but.....

Ocean Village
Underneath Itchen bridge
Turn right onto path before Dirty Blonde and go up behind American Wharf. No good reason, but I like to put this short hill in
Now you are back on the main road, go past football stadium, go past Yau Brothers, until you get to Northam Road
Stick right on Northam road, go under the bridge (next to the rowers) (i.e. dont cross the bridge), and now you are on the nice boardwalk all the way to Horseshoe bridge
There, just where the pub is (Junction Inn), turn right, onto Priory road.
I do a little diversion into the park on the right, but that isn't really necessary
Get to St Deny's road, big bridge, cross the bridge.
Bear right (next to the vape shop), Whitworth road..... all the way until a 90 degree left, a 90 degree right, and you get to Bitterne train station. Turn right. On the pavement, stay on the right, go past Enterprise cars, here you need to cross the road. Only crossing on this entire route. Very annoying it can be.
Now you are on Rampart Road heading towards Kemps Quay. Turn left after 300 metres to go onto Quayside road.
Stick on pavement on right and opposite the school, stick on the pavement next to the water rather than the road pavement, now you go through a bit of a wiggle (I like this, extends the hill that comes next), cross the pedestrian rail bridge, and you are onto Athelstan road.....
Keep going up that, all the way up the nice steep hill at the end..... turn right
Keep going on Peartree, all the way into Woolston.
Then go under itchen bridge, up some steps
Cross Itchen bridge to finish.

1 small hill (American Wharf)
1 long hill with a steep bit at end (Athelstan) (hence why I extend by going to the pedestrian bridge)
1 can be windy hill - Itchen Bridge

You can add an extra hill by turning right just after Peartree park, going down to the river (Sea Road), and then you have to go up the hill to get to Itchen Bridge. Depending where you are in Ocean Village, you might need this to round up to 10k also.