I'm building a scene on an 8x8 base plate, ideally the depth of the base is 1 full brick high. The design is to have a swimmer minifig horizontal (i.e. swimming) but also at an angle to the base plate, and ideally connected, not just laid on top. I can achieve the angle with a 2x2 turntable plate, and get the swimmer horizontal with a 1x2 hinge brick on top of the turntable, but this makes the swimmer quite high. Any ideas on how to achieve the same - I'm wondering if a torso attachment on the hidden underside of the minifig might work but can't think what piece to use.
Mmmh... If you base doesn't have to be all solid...
Recess some piece in there in which you can insert the arm-side of a mini-fig hand.
Grasp your swimmer by the toes on one of its feet, with that hand.
That will give you a horizontal/slightly upwards position on the mini-fig and you can further increase the angle by adjusting the mini-figs leg.
There are several pieces which can be attached to minifigures to pose them. Recently a line of collectible minifigures introduced a transparent "handle" with a single stud which could be connected to the feet or legs of the minifigure
This piece can be rotated in the anti-stud to angle whichever way is convenient, then held in place using a hole or clip.