After market seat

you can do this with shorter shocks or you can have the seat custimized if you cut foam off hieght of seat and you will not have to lower the bike it maybe cheaper to do the seat

Only two ways you can acheive this. the first is to have your rear suspension modified, or lowered by about an inch should do it. This job would most likely have to be done at a mechanics shop. But is possible.
The second solution, involves lowering your seat height, by cutting about an inch or so of foam off the top of the seat. This job is also best done by an upholsterer, but is a possible aternative to lowering the suspension, get your seat chopped down.

depending how much you want to adjust ,if you need it lowering a bit you could see if you can cut some foam out the seat you just use a electric carving knive

I'd check to see if it has a clutch safety switch

You may be able to modify your seat by removing some of the padding, and recovering it. Aftermarket seats may also be available.

Very slight adjustments in height can often be achieved by moving the fork tubes in the triple clamp. Note that this will affect the handling characteristics of the bike. This modification is not recommended for safety reasons.

Another alternative is to wear boots with an extra thick sole.

In any of these cases, the difference in height is going to be relatively small -- a couple inches at most. It is important that your bike allows you to feel comfortable, confident, and that you can control it fully at all times. Although it's not a very satisfying solution, the best solution might be to find a bike with a lower standover height.

about 2L to 2.5L of oil and do it slowly it overfills very fast

you could try a little bit smaller rear tire. cheaper than the shocks maybe

best go with a lowering link to drop the rear end a little. there is not much seat there in the first place for anyone to make a thinner one, other than getting a race use seat unit. http://www.mpsracing.com/products/Spencer/Links.asp