Hi Ken:
Welcome to the forums!!!
I have no idea what your knowledge and skill levels are so I will just throw in my worth.
Derailments and unwanted uncoupling can be prevented if you are prepared to spend the time bringing your rolling stock up to NMRA RPs (Recommended Practises) and fine tuning your track. Perhaps you have tried that already.
Unwanted uncoupling can be caused by not having all your couplers at exactly the same height. Kadee sells a couple of different gauges to measure coupler height. They are essentially the same but one is insulated so you can put it on live track. Coupler height becomes more important when there is a grade change. Plastic couplers can flex a bit which may contribute to missalignment, especially on long trains.
Derailing can be caused by flaws in the track. Even though your track may look good from your normal viewing perspective, getting down and eyeing the track to see if there are any minor kinks is a good thing to do. Also, taking pictures down the track can show a lot that the naked eye can't see.
Another cause for derailing is not having the trucks pivoting properly. If a truck is stiff it can easily ride up over the rails. Car weight also come into play. The NMRA has an RP that suggests the weight for various length cars. It is basically 1 oz. + 1/2 oz for every 1" of car length. If you have some lightweight cars close to the front of a longer train they can be pulled off the track in the curves.
As for O gauge, I know nothing other than that it is apparently expensive. If you are into detailing you can do some really fine stuff though.
The important thing is to be happy. Model railroading is supposed to be fun. If you are not having fun in HO then perhaps you should try O.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
I am 67 and have gotten back into model railroading for about the last 4 years. I've begun with an HO layout which is approximately 6 1/2' x20'. with a few grades here and there. I have trouble with cars derailing after rounding the track 20 or 30 times flawlessly. Also have trains break apart at the couplers at varius times. I have been considering changing to O gauge to eliminate all this frustration. I do have an old Lionel 027 train set from the late 40's so I would have something to start with. Would you consider making this change? I do have quite a bit of work involved in the HO layout but it has been so frustrating I am loosing interest and haven't made much progress this past winter since I've been considering this change. What would be the pros and cons of making this switch?