How much setback does your current seatpost have?

25mm setback on a post is pretty standard. Zero offset posts are available and some seatposts come with35-40mm of offset. What's being measure here is from the centre of the seatpost to the CENTRE of the saddle clamps.

If you already have a standard seatpost with 25mm of setback it going to be near impossible to find a seatpost with a FURTHER 25mm of extra setback.
Something to keep in mind here is the width of the clamps. 2 different seatposts can have the same nominal setback but if one of the posts has narrower clamps it is possible to position the seat further back.

Anthony