Are there standard visual cues or other methods for flaring in a B737-800?
I'm not sure I understand what you're asking, but proceeding from what I think you may be asking, consider the following.

Are you flaring from a stabilized approach? Until a pilot internalizes things for any large aircraft, using a stabilized approach on speed appropriate to your landing weight gives a common, starting reference to work from.

From such an approach you should have been given in training the altitude from which to start the flare. For purposes of discussion, let's say that's the 50 feet you mentioned. Thus, the first problem is determining when you're at that point. Assuming you have a radar altimeter, are you using the call outs from the altimeter to consistently start the flare at the same altitude?

Now, in a stabilized approach, you don't feel a change in sink rate in the seat of your pants until you actually start the flare, so when you say "the sink feels too much", I'm assuming that you're having trouble with the rate of your flare. In other words, how much back pressure you should be exerting on the yoke. My thought would be that you could try focusing on how much to raise the nose at the 50 foot call rather than trying for a given amount of feel in the seat of your pants. I never flew the 737, but on the 747, at the 50 foot call, I would would raise the nose to 5&deg; higher than it was during the stabilized approach. Then at the 10 foot call, I would raise it 2&deg; higher yet. There would, of course, be an appropriate power reduction each time.

The 737 will have different numbers than the 747, but what I'm suggesting is to try doing it by the numbers, consistently, every time. Any 737 instructor should be able to tell you what those numbers are. You might even try posting a question here asking specifically what those numbers are. Perhaps a 737 pilot will see this answer and provide them.

Finally, an advantage of doing things by the numbers is that it really doesn't matter what your seat position is, although you should certainly go for a seat position that will eventually allow you to best internalize what the numbers mean insofar as the view out the windshield. When I transitioned from the F-27 to the SA-227, I found the view out the front confusing, but no matter since they taught us to simply do it by the numbers at first.

My apologies if my answer has been too pedantic or if I have misunderstood the question. If so, let me know in a comment and I'll be happy to delete the answer.