700C suspension fork

Hi, I would really appreciate some advice on this.
I have a Marin rigid aluminium framed so called hybrid with a carbon fork and 700c wheels.
I ride alot on hard pack trails and the actual roads are often worse. On rides over 50 miles I find the vibration and general shocks from the front very tiring - I seem to put a lot of weight on the bars - so I am thinking of a light suspension front fork. It doesn't need to have a lot of travel.

I know there are 1 or 2 shocks out there that will take a 700C wheel. What I am worried about  ??? is how it will affect the steering and other aspects of the geometry - the front of the bike will be alittle higher than it is now, so the head tube angle will be lower, the bottom bracket will be higher etc. The head tube is 71degrees at present which seems pretty relaxd.

Any advice?  Thanks for your help,
C_hawk