A lubricant is meant to replace arousal fluid, not cervical fluid. Lubricants should only be used while trying to conceive if you cannot have sex comfortably without one. No lubricants, even ones that claim to be sperm-friendly or sperm-neutral, are meant to be a replacement for cervical fluid and most are unfriendly to sperm.
Saliva is also unfriendly to sperm and should not be used as a lubricant while trying to conceive.
If you must use a lubricant to have intercourse, check with your doctor or pharmacist to find the one that is right for you that will be most friendly to sperm. Keep in mind though that no lubricant enhances your chances of conception. A lubricant can only help you conceive if you would not or could not have intercourse without it.
Additionally, when using a lubricant, you may find that identifying your cervical fluid type is more challenging as the lubricant may mask your cervical fluid. If you are in doubt about your cervical fluid type and it is a potentially fertile time, record "egg white" or "watery" so that it is recognized as a potentially fertile day. It is also recommended to record your use of the lubricant in the notes section of your chart so that you will be able to identify a potential cause for any unusual observations.