I can not advise you about what the creditor (or the debt collector) can execute on under state law and do not know everything you own. Often, the debt collectors have run computer routines in order to select people they are most likely to collect from.
If you're on SSDI, you may qualify for assistance from your local legal services provider and should contact them immediately if you are sued.
If a third party debt collector is contacting you, you should contact a MO attorney who represents consumers in cases against debt collectors under the Fair Debt Collection Practices Act ("FDCPA") so that you understand your rights.
If you want to know what assets are exempt under MO law based upon your specific situation, contact a local bankruptcy attorney. They work with the exemptions every case they file.