Based on your description, you are dealing with this staining in an appropriate manner.
As long as you do not experience an actual flow, you may continue taking precautions against becoming niddah from this spotting by wearing colored underwear (or disposable pantyliners) and waiting 15 seconds after urinating before wiping.
It is not considered cheating or tricking the system to avail yourself of these leniencies. When the rabbis decreed that stains render women niddah, they included these leniencies so that women would not find themselves in a constant state of niddah. As long as the stains are on colored underwear, pantyliners, or on toilet paper (not immediately after urinating) you may continue to disregard them.
It actually may be a good idea to check your toilet paper in your situation (taking care to wait 15 seconds after urinating) so you can be aware of whether you are actively staining or not. If you find it difficult to remember to wait 15 seconds, then it may be better to avoid looking at the toilet paper so you don't accidentally become niddah from a problematic stain.
In a situation of staining we do advise abstaining from intercourse until about 24 hours after the staining subsides. This is a precaution to avoid the halachically complex situation of finding blood during or immediately after intercourse, which would make you niddah and could have additional halachic implications.
It is important to note that while this is our recommendation, it is not halachically required, and in certain situations you can use your judgement to be intimate even without waiting 24 hours. For example, in perimenopause, or when using the minipill, when staining is frequent and the 24 hour rule may make it close to impossible to actually be intimate, you can check externally for any staining (by wiping with a tissue, not after urinating) prior to intimacy without actually waiting 24 hours. If the tissue is clear, go ahead with intercourse. If it is stained, you are not rendered niddah, but should wait another 6-12 hours before trying again.
After intercourse wait a few minutes before getting up and/or wiping or cleaning yourselves. Do not look for any staining and be sure to use disposable tissues or a colored towel to wipe yourselves. Make sure your bedding is colored as well. Be sure to wait 15 seconds after urinating and don't look down while on the toilet so you don't accidentally see any blood exiting your body. Your husband should also clean himself off without looking.
We generally recommend allowing a few months for your body to adjust to any form of hormonal contraception. While some women manage fine on the minipill despite the staining, for some women the staining cause too much difficulty (whether rendering them niddah frequently, or affecting intimacy due to constant staining, etc.). In those situations, it may be worthwhile consulting with a doctor as to whether there is a better option for birth control (such as the diaphragm or combined pill).
Please feel free to get back to us with any further questions.