Given your motherboard's limitations regarding NVMe slots, using an adapter or enclosure for NVMe drives through your external SATA port could be a viable solution. However, ensure compatibility with your motherboard and consider the performance implications. Alternatively, if you're open to traditional HDDs, a high-capacity 2TB spinner could meet your storage needs economically. This option may lack the speed of SSDs but could offer ample storage at a lower cost. Another consideration is the reliability of your storage solutions. If you've experienced failures with your drives in the past, investing in reliable storage options, whether SSDs or HDDs, is crucial to safeguard your data. Ultimately, weigh factors such as speed, capacity, cost, and reliability when choosing your storage solution, and consider future upgrade paths for your system's storage capabilities.