Besides the Livonian Rhymed Chronicle and Henry of Livonia, there isn't much I can find. I've been writing something for my own pleasure, and need some primary sources as I've mostly been sourcing The Northern Crusades by Eric Christiansen as well as other authors such as Peter Lock, the book Livonia, Rus’ and the Baltic Crusades in the Thirteenth Century by Anti Selart and the companion to the chronicle of Henry by Carsten Selch Jensen and co, all of which, I'm sure you know, are secondary sources.
Does anyone have anything they can point me to regarding, say, writings about Albert of Riga by his contemporaries or some stuff about the Livonian Sword brothers? Sorry if this seems like a long-winded question, I just can't really find anything besides the Rhymed Chronicle and the Chronicle of Henry. Any answers are appreciated, I just need to be pointed in the right direction really.
On the whole, the Northern Crusades aren't as well documented as most of the arguably more famous Crusades to the Holy Land. However, there are still some fantastic sources out there. To my knowledge, the chronicles written by Henry of Livonia and Helmold are the most detailed. Excerpts of the sources I have listed below are easily accessible in Allen and Amt's fantastic The Crusades: A Reader (second edition):
The Chronicle of Henry of Livonia - trans. J.A. Brundage, The Chronicle of Henry of Livonia (Madison: University of Wisconsin Press, 1961).
Helmold's Chronicle of the Slavs - trans. F.J. Tschan, The Chronicle of the Slavs by Helmld, Priest of Bosau (New York: Octagon Books, 1966).
Nikolaus von Jeroschin on the Prussian Crusades - trans. H.F. Schwarz, Ordensritter und Kirchenfürsten, ed. J. Bühler (Berlin: Insel-Verlag, 1927).
The Rule of the Teutonic Knights - trans. I. Sterns, "The Statutes of the Teutonic Knights: A Study of Religious Chivalry" (Philadelphia: University of Pennsylvania, unpublished Ph.D. dissertation, 1969).