Well, honestly, unless you plan to format the entire drive and use all of the capacity, running trim on SSD is not really super-important (most drives have built-in garbage collection). You could in theory boot into Linux for trim, but the problem is that most modern Linux distros require stuff like i686, or PAE/NX support...which is not present in your system. Don't forget that Windows 7 (32 bits) also require more RAM than your machine is likely to support, and the process of booting into it will probably require more swapping (that's just adding more writes on a machine than regular Win98 will ever do). Instead, consider over provisioning and under-utilizing. Buy a 128GB SSD and format only for a single 30GB FAT32 partition for Win98, so your total utilization will never exceed even 30% of the total drive. On my Thinkpad T21 (with 512MB of RAM and running Win98SE, good luck getting it to swap on most things) the 128GB mSATA SSD (with a 44 pin adapter/enclosure) is only formatted to use a 16GB partition, which in itself is only about 5 GB used. With light to medium usage I do not expect it to give me issues whatsoever for the next few years. Plus the intention was not only to improve performance as sustained writes are only about 25MBytes/sec (so not too far off the original - although reads and random reads/writes do perform much better) - it's really to get rid of a mechanical device with questionable long term viability and replace it with something that should fare better in the long run. MSATA to IDE tends to perform better than the CF/SD to IDE cards.

CF to IDE? Not a bad idea. Although I actually use an MicroSD to CF/IDE adapter on one of my 5x86 class thin clients running Windows 98 - that IDE implementation is poor to begin with so the media (as long as it's a class A2/V10 card) is not a bottleneck. The SD card just makes it easier for me to image it out via Clonezilla for archival purposes. Long term viability of most SD cards are questionable, but if you image and swap on a regular basis this concert should be minimal. I just happen to like it because of how easy it is to pop the SD card off the CF adapter in case I need to test things. Just remember that the common JMicron SD/CF to IDE adapter bridge chips have a practical limit of about 25MBytes/sec sustained writing, so don't expect it to pull miracles.

IDE SSDs are rather expensive as far as I can tell. However you can use a 2,5" IDE-mSATA converter like this one plus an mSATA SSD.

Don't worry too much about TRIM on Win98. The important thing are wear leveling and garbage collection and those are handled by the flash controller.TRIM is a nice feature for newer operating systems which constantly write large amounts of data to the drive because it keeps the drive snappy. Depending on the flash controller TRIM can also help reduce wear during garbage collection but mostly it improves drive speed. It tells the controller which flash blocks no longer contain any data without the controller having to check the block first. The flash block is either overwritten or simply marked as empty so with the next write it can be simply written to without being checked for relevant data first. This is why without TRIM SSDs will get a bit slower with time but only to a certain degree.
With Win98 and especially on your notebook you shouldn't notice this (except maybe in synthetic benchmarks). The software can't take advantage of the additional speed and the rest of the system is much more of a limiting factor anyway. Win98 also stresses the drive much less than current OS so wear in general isn't that much of a concern if you use those systems for gaming.

Generally speaking a current SSD with DRAM cache run with Win98 inside a gaming system is likely to last as long as the notebook you are going to put it into. 😀