Welcome!!
The other option would be to try to raise him as modern Orthodox, but that is not our first choice because they do not have the matchmaking system in place for marriage purposes that ultra-orthodox people do.
The choice of how you want your son to grow – Modern orthodox or ultra-orthodox – should not be based on a matchmaking system. Conveniences and practicalities pale in the bigger picture when discussing something as large as the Yiddishkeit of your children – and their generations to come. You should sit and think – seriously think – about your level of commitment to Avoidas Hashem, and whether you are able to commit to ultra orthodox. If you can, אשריך וטוב לך.
It is also been my experience that of the people that I know who are divorced something like 90% of them are modern Orthodox even though they are no more than 30% of our community.
Just to echo my previous point – this shouldn’t be the reason to become Ultra Orthodox over Modern Orthodox. It is more likely to be an indication of other issues, however, which should be weighed into your decision.